Add TurboVNC encoding support.

TurboVNC is a variant of TightVNC that uses the same client/server protocol (RFB version 3.8t),
and thus it is fully cross-compatible with TightVNC and TigerVNC (with one exception, which is noted below.)
Both the TightVNC and TurboVNC encoders analyze each rectangle, pick out regions of solid color to send
separately, and send the remaining subrectangles using mono, indexed color, JPEG, or raw encoding, depending
on the number of colors in the subrectangle.  However, TurboVNC uses a fundamentally different selection
algorithm to determine the appropriate subencoding to use for each subrectangle.  Thus, while it sends a
protocol stream that can be decoded by any TightVNC-compatible viewer, the mix of subencoding types in this
protocol stream will be different from those generated by a TightVNC server.

The research that led to TurboVNC is described in the following report:
http://www.virtualgl.org/pmwiki/uploads/About/tighttoturbo.pdf.
In summary:  20 RFB captures, representing "common" 2D and 3D application workloads (the 3D workloads were
run using VirtualGL), were studied using the TightVNC encoder in isolation.  Some of the analysis features
in the TightVNC encoder, such as smoothness detection, were found to generate a lot of CPU usage with little
or no benefit in compression, so those features were disabled.  JPEG encoding was accelerated using
libjpeg-turbo (which achieves a 2-4x speedup over plain libjpeg on modern x86 or ARM processors.)  Finally,
the "palette threshold" (minimum number of colors that the subrectangle must have before it is compressed
using JPEG or raw) was adjusted to account for the fact that JPEG encoding is now quite a bit faster
(meaning that we can now use it more without a CPU penalty.)  TurboVNC has additional optimizations,
such as the ability to count colors and encode JPEG images directly from the framebuffer without first
translating the pixels into RGB.  The TurboVNC encoder compares quite favorably in terms of compression
ratio with TightVNC and generally encodes a great deal faster (often an order of magnitude or more.)

The version of the TurboVNC encoder included in this patch is roughly equivalent to the one found in version
0.6 of the Unix TurboVNC Server, with a few minor patches integrated from TurboVNC 1.1.  TurboVNC 1.0
added multi-threading capabilities, which can be added in later if desired (at the expense of making
libvncserver depend on libpthread.)

Because TurboVNC uses a fundamentally different mix of subencodings than TightVNC, because it uses
the identical protocol (and thus a viewer really has no idea whether it's talking to a TightVNC or
TurboVNC server), and because it doesn't support rfbTightPng (and in fact conflicts with it-- see below),
the TurboVNC and TightVNC encoders cannot be enabled simultaneously.

Compatibility:

In *most* cases, a TurboVNC-enabled viewer is fully compatible with a TightVNC server, and vice versa.
TurboVNC supports pseudo-encodings for specifying a fine-grained (1-100) quality scale and specifying
chrominance subsampling.  If a TurboVNC viewer sends those to a TightVNC server, then the TightVNC server
ignores them, so the TurboVNC viewer also sends the quality on a 0-9 scale that the TightVNC server can
understand.  Similarly, the TurboVNC server checks first for fine-grained quality and subsampling
pseudo-encodings from the viewer, and failing to receive those, it then checks for the TightVNC 0-9
quality pseudo-encoding.

There is one case in which the two systems are not compatible, and that is when a TightVNC or TigerVNC
viewer requests compression level 0 without JPEG from a TurboVNC server.  For performance reasons,
this causes the TurboVNC server to send images directly to the viewer, bypassing Zlib.  When the
TurboVNC server does this, it also sets bits 7-4 in the compression control byte to rfbTightNoZlib (0x0A),
which is unfortunately the same value as rfbTightPng.  Older TightVNC viewers that don't handle PNG
will assume that the stream is uncompressed but still encapsulated in a Zlib structure, whereas newer
PNG-supporting TightVNC viewers will assume that the stream is PNG.  In either case, the viewer will
probably crash.  Since most VNC viewers don't expose compression level 0 in the GUI, this is a
relatively rare situation.

Description of changes:

configure.ac
-- Added support for libjpeg-turbo.  If passed an argument of --with-turbovnc, configure will now run
   (or, if cross-compiling, just link) a test program that determines whether the libjpeg library being
   used is libjpeg-turbo.  libjpeg-turbo must be used when building the TurboVNC encoder, because the
   TurboVNC encoder relies on the libjpeg-turbo colorspace extensions in order to compress images directly
   out of the framebuffer (which may be, for instance, BGRA rather than RGB.)  libjpeg-turbo can optionally
   be used with the TightVNC encoder as well, but the speedup will only be marginal (the report linked
   above explains why in more detail, but basically it's because of Amdahl's Law.  The TightVNC encoder
    was designed with the assumption that JPEG had a very high CPU cost, and thus JPEG is used only sparingly.)
-- Added a new configure variable, JPEG_LDFLAGS.  This is necessitated by the fact that libjpeg-turbo
   often distributes libjpeg.a and libjpeg.so in /opt/libjpeg-turbo/lib32 or /opt/libjpeg-turbo/lib64,
   and many people prefer to statically link with it.  Thus, more flexibility is needed than is provided
   by --with-jpeg.  If JPEG_LDFLAGS is specified, then it overrides the changes to LDFLAGS enacted by
   --with-jpeg (but --with-jpeg is still used to set the include path.)  The addition of JPEG_LDFLAGS
   necessitated replacing AC_CHECK_LIB with AC_LINK_IFELSE (because AC_CHECK_LIB automatically sets
   LIBS to -ljpeg, which is not what we want if we're, for instance, linking statically with libjpeg-turbo.)
-- configure does not check for PNG support if TurboVNC encoding is enabled.  This prevents the
   rfbSendRectEncodingTightPng() function from being compiled in, since the TurboVNC encoder doesn't
   (and can't) support it.

common/turbojpeg.c, common/turbojpeg.h
-- TurboJPEG is a simple API used to compress and decompress JPEG images in memory.  It was originally
   implemented because it was desirable to use different types of underlying technologies to compress
   JPEG on different platforms (mediaLib on SPARC, Quicktime on PPC Macs, Intel Performance Primitives, etc.)
   These days, however, libjpeg-turbo is the only underlying technology used by TurboVNC, so TurboJPEG's
   purpose is largely just code simplicity and flexibility.  Thus, since there is no real need for
   libvncserver to use any technology other than libjpeg-turbo for compressing JPEG, the TurboJPEG wrapper
   for libjpeg-turbo has been included in-tree so that libvncserver can be directly linked with libjpeg-turbo.
   This is convenient because many modern Linux distros (Fedora, Ubuntu, etc.) now ship libjpeg-turbo as
   their default libjpeg library.

libvncserver/rfbserver.c
-- Added logic to check for the TurboVNC fine-grained quality level and subsampling encodings and to
   map Tight (0-9) quality levels to appropriate fine-grained quality level and subsampling values if
   communicating with a TightVNC/TigerVNC viewer.

libvncserver/turbo.c
-- TurboVNC encoder (compiled instead of libvncserver/tight.c)

rfb/rfb.h
-- Added support for the TurboVNC subsampling level

rfb/rfbproto.h
-- Added constants for the TurboVNC fine quality level and subsampling encodings as well as the rfbTightNoZlib
   constant and notes on its usage.
Fix an issue that affects the existing Tight encoder as well as the newly-implemented Turbo encoder.

The issue is that, when using the current libvncserver source, it is impossible to disable Tight JPEG encoding.
The way Tight/Turbo viewers disable JPEG encoding is by simply not sending the Tight quality value, causing the
server to use the default value of -1.  Thus, cl->tightQualityLevel has to be set to -1 prior to processing the
encodings message for this mechanism to work.  Similarly, it is not guaranteed that the compress level will be
set in the encodings message, so it is set to a default value prior to processing the message.
Fix the build of x11vnc when an out-of-tree build directory is used
Move tightsubsamplevel member to the end of rfbClient struct.

Try to not break ABI between releases. Even if the code gets ugly...
Add DRC to AUTHORS.
Replace TightVNC encoder with TurboVNC encoder. This patch is the result of further research and discussion that revealed the following:

-- TightPng encoding and the rfbTightNoZlib extension need not conflict.  Since
   TightPng is a separate encoding type, not supported by TurboVNC-compatible
   viewers, then the rfbTightNoZlib extension can be used solely whenever the
   encoding type is Tight and disabled with the encoding type is TightPng.

-- In the TightVNC encoder, compression levels above 5 are basically useless.
   On the set of 20 low-level datasets that were used to design the TurboVNC
   encoder (these include the eight 2D application captures that were also used
   when designing the TightVNC encoder, as well as 12 3D application captures
   provided by the VirtualGL Project--
   see http://www.virtualgl.org/pmwiki/uploads/About/tighttoturbo.pdf), moving
   from Compression Level (CL) 5 to CL 9 in the TightVNC encoder did not
   increase the compression ratio of any datasets more than 10%, and the
   compression ratio only increased by more than 5% on four of them.  The
   compression ratio actually decreased a few percent on five of them.  In
   exchange for this paltry increase in compression ratio, the CPU usage, on
   average, went up by a factor of 5.  Thus, for all intents and purposes,
   TightVNC CL 5 provides the "best useful compression" for that encoder.

-- TurboVNC's best compression level (CL 2) compresses 3D and video workloads
   significantly more "tightly" than TightVNC CL 5 (~70% better, in the
   aggregate) but does not quite achieve the same level of compression with 2D
   workloads (~20% worse, in the aggregate.) This decrease in compression ratio
   may or may not be noticeable, since many of the datasets it affects are not
   performance-critical (such as the console output of a compilation, etc.)
   However, for peace of mind, it was still desirable to have a mode that
   compressed with equal "tightness" to TightVNC CL 5, since we proposed to
   replace that encoder entirely.

-- A new mode was discovered in the TurboVNC encoder that produces, in the
   aggregate, similar compression ratios on 2D datasets as TightVNC CL 5.  That
   new mode involves using Zlib level 7 (the same level used by TightVNC CL 5)
   but setting the "palette threshold" to 256, so that indexed color encoding
   is used whenever possible.  This mode reduces bandwidth only marginally
   (typically 10-20%) relative to TurboVNC CL 2 on low-color workloads, in
   exchange for nearly doubling CPU usage, and it does not benefit high-color
   workloads at all (since those are usually encoded with JPEG.)  However, it
   provides a means of reproducing the same "tightness" as the TightVNC
   encoder on 2D workloads without sacrificing any compression for 3D/video
   workloads, and without using any more CPU time than necessary.

-- The TurboVNC encoder still performs as well or better than the TightVNC
   encoder when plain libjpeg is used instead of libjpeg-turbo.

Specific notes follow:

common/turbojpeg.c common/turbojpeg.h:
Added code to emulate the libjpeg-turbo colorspace extensions, so that the
TurboJPEG wrapper can be used with plain libjpeg as well.  This required
updating the TurboJPEG wrapper to the latest code from libjpeg-turbo 1.2.0,
mainly because the TurboJPEG 1.2 API handles pixel formats in a much cleaner
way, which made the conversion code easier to write.  It also eases the
maintenance to have the wrapper synced as much as possible with the upstream
code base (so I can merge any relevant bug fixes that are discovered upstream.)
The libvncserver version of the TurboJPEG wrapper is a "lite" version,
containing only the JPEG compression/decompression code and not the lossless
transform, YUV encoding/decoding, and dynamic buffer allocation features from
TurboJPEG 1.2.

configure.ac:
Removed the --with-turbovnc option.  configure still checks for the presence of
libjpeg-turbo, but only for the purposes of printing a performance warning if
it isn't available.

rfb/rfb.h:
Fix a bug introduced with the initial TurboVNC encoder patch.  We cannot use
tightQualityLevel for the TurboVNC 1-100 quality level, because
tightQualityLevel is also used by ZRLE.  Thus, a new parameter
(turboQualityLevel) was created.

rfb/rfbproto.h:
Remove TurboVNC-specific #ifdefs and language

libvncserver/rfbserver.c:
Remove TurboVNC-specific #ifdefs.  Fix afore-mentioned tightQualityLevel bug.

libvncserver/tight.c:
Replaced the TightVNC encoder with the TurboVNC encoder.  Relative to the
initial TurboVNC encoder patch, this patch also:
-- Adds TightPng support to the TurboVNC encoder
-- Adds the afore-mentioned low-bandwidth mode, which is mapped externally to
   Compression Level 9

test/*:
Included TJUnitTest (a regression test for the TurboJPEG wrapper) as well as
TJBench (a benchmark for same.)  These are useful for ensuring that the wrapper
still functions correctly and performantly if it needs to be modified for
whatever reason.  Both of these programs are derived from libjpeg-turbo 1.2.0.
As with the TurboJPEG wrapper, they do not contain the more advanced features
of TurboJPEG 1.2, such as YUV encoding/decoding and lossless transforms.
Extend support for the new TurboVNC encoder to the CMake build system
Fix memory leak in TurboVNC

Note that the memory leak was only occurring with the colorspace
emulation code, which is only active when using regular libjpeg (not
libjpeg-turbo.)

Diagnosed by Christian Beier, using valgrind.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Make TurboVNC compress level 3 actually work.
LibVNCClient: properly free the openssl session stuff on shutdown.
LibVNCClient: Fix build with no SSL/TLS library available.
Add Philip to AUTHORS.
Added support for UltraVNC Single Click as originally proposed by Noobius (Boobius) on 6/1/11.

Original thread: http://sourceforge.net/tracker/?func=detail&aid=3310255&group_id=32584&atid=405860
Fix compilation with some libjpeg distributions.
Fix turbojpeg tests compilation.
Merge branch 'turbovnc'

Conflicts, resolved manually:
	AUTHORS
Fix some compiler warnings thrown with newer gcc.
Bump version to 0.9.9.
Binaries that are to be installed should be all lowercase.
Better check for Linux build.