Update Libav API uses

Change various code to use the latest Libav API. The libavcodec
error_recognition setting has been removed and replaced with different
semantics. I removed the "--lavdopts=er=<value>" option accordingly,
as I don't think it's widely enough used to be worth attempting to
emulate the old option semantics using the new API. A new option with
the new semantics can be added later if needed.

Libav dropped APIs that were necessary with all Libav versions
until quite recently (like setting avctx->age), and it would thus not
be possible to keep compatibility with previous Libav versions without
adding workarounds. The new APIs also had some bugs/limitations in the
recent Libav release 0.8, and it would not work fully (at least some
avcodec options would not be set correctly). Because of those issues,
this commit makes no attempt to maintain compatibility with anything
but the latest Libav git head. Hopefully the required fixes and
improvements will be included in a following Libav point release.
demux_lavf: use Libav RIFF tag lists directly

Change demux_lavf to use CodecID -> RIFF tag mappings that are now
available through the public Libav API. Previously it used a copy in
ffmpeg_files/taglists.c. That can now be deleted.
build: switch to libavutil bswap.h and intreadwrite.h

Remove the private bswap and intreadwrite.h implementations and use
libavutil headers instead.

Originally these headers weren't publicly installed by libavutil at
all. That already changed in 2010, but the pure C bswap version in
installed headers was very inefficient. That was recently (2011-12)
improved and now using the public bswap version probably shouldn't
cause noticeable performance problems, at least if using a new enough
compiler.
vd_ffmpeg: adjust buffered frame count based on threads again

Libav has changed back to not modifying avctx->has_b_frames based on
the extra buffering caused by thread use. Add back the code to do the
adjustment on the player side once again.

The timing mode using the buffering info is no longer the default, so
in most cases having this right or not won't matter for playback.
vd_ffmpeg: fix flushing of buffered frames

The vd_ffmpeg decode() function returned without doing anything if the
input packet had size 0. This meant that flushing buffered frames at
EOF did not work. Remove this test. Have the core code skip such
packets coming from the file being played instead (Libav treats
0-sized packets as flush signals anyway, so better assume such packets
do not represent real frames with any codec).
screenshot: fix libav API use (pix_fmt and some other things)

Libavcodec started checking that avctx->pix_fmt is set when opening
an encoder. The existing code (originally from vf_screenshot.c) only
set it afterwards, which now made screenshots fail. Fix the code to
set parameters before calling avcodec_open2().

Also fix some minor things, which seems to make it work for other
encoders. This could be used to add more libavcodec based image
writers. Fix memory leak (missing av_free(avctx)).
osd: erase terminal OSD line with mp_msg() instead of printf()

The terminal OSD line was written with mp_msg(MSGT_CPLAYER, ...) but
erased with printf(). This meant that disabling MSGT_CPLAYER messages
would prevent the terminal line from being printed, but a line
(probably unrelated) would still be cleared. Change the clearing code
to use mp_msg(MSGT_CPLAYER, ...) too.
demux_lavf: update growing file size info for AVSEEK_SIZE

demux_lavf was returning a static size value when libavformat queried
file size with AVSEEK_SIZE. Add code to query the stream for possibly
changed value first. This at least improves seeking with growing MPEG
files; before seeks would never go beyond the part of the file that
existed when the stream was first opened.
configure: simplify pkg-config handling, drop other tests

Add helper function pkg_config_add() that checks for the presence of a
package and also adds cflags/ldflags if it is found. Change existing
pkg-config-using feature tests to use that. Also change the freetype
test that used a separate libfreetype-config binary before; using
pkg-config instead helps cross-compiling. Drop other kinds of checks
(such as test compiles) from these tests. It's possible that this
could cause problems on some (broken) systems, but that can't be
verified without user testing.
configure, ao_alsa: drop support for obsolete ALSA versions

Drop compatibility code for ALSA versions prior to 1.0.9. Change the
configure check to use pkg-config only.
configure, build: support compiling without libpostproc

libpostproc has been removed from Libav and the library now exists as
a separate project. Because it's not essential, separate it from the
Libav library check and allow compiling without it.
vo: reject vo_redraw_frame() if no frames have been drawn

vo_xv crashed if existing frames had been lost due to a config() call
in the middle of a file and vo_redraw_frame() was called. Add checks
to reject vo_redraw_frame() unless at least one frame has been flipped
after the the last configuration change, so individual VOs do not have
to deal with this case.
configure: remove obsolete messages for mtrr / no w32codecs

Remove "Please check mtrr settings at /proc/mtrr" and "NOTE: Win32
codec DLLs are not supported on your CPU" messages printed at the end
of a configure run. mtrr should be irrelevant on today's machines, and
the DLLs are a lot less important nowadays. Also remove mtrr detection
logic that was only used to decide whether or not to print that
message. Bizarrely, there were --enable-mtrr and --disable-mtrr
options for this too (with no effect except for the message).
vo_png: set AVCodecContext parameters before opening it

Instead of opening avctx in preinit() and setting paramters later,
(re)open it in config() where parameters can be set first. This fixes
a failure to open the codec with new libavcodec versions that check
pix_fmt during avcodec_open2().
aviheader.c: silence a warning

libmpdemux/aviheader.c:235:7: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
configure: show PKG_CONFIG_PATH and CFLAGS in config.log

When the build wrapper repo scripts run configure they set a custom
PKG_CONFIG_PATH environment variable. Show the value of this in
config.log to make it easier to rerun configure with a tweaked version
of the same parameters. Also show CFLAGS if set, as it's likely to
break things.
configure: fix target triplet check for mingw targets

mingw32 and mingw64's recommended triplets are i686-pc-mingw32 /
x86_64-w64-mingw32, neither has mingw32 in the middle.
configure: disable cross compilation auto detection

This didn't work very well when cross compiling from Linux to Windows:
it tries to execute an .exe file, which succeeds if wine is installed.
As consequence it detects "no" as result.

In general this won't work if emulation for the target architecture is
available. Remove it.
configure: use cross toolchain if --target is given

If --enable-cross-compile is specified, passing
--target=i686-w64-mingw32 for example will check if
i686-w64-mingw32-gcc can be used. This is only done if the compiler
isn't specified via --cc or the CC environment variable.

The same is done for some other build tools, such as pkg-config.
(Only the C compiler will try to use a fallback in this case.)
configure: allow changing pkg-config binary with --pkg-config