core: timeline: prevent inaccurate seeks outside timeline

Ensure that even if a seek is inaccurate it will not show video from
outside the defined timeline. Previously, seeking to the beginning of
a segment could show frames from before the start of the segment if
the seek was done in inaccurate mode and the demuxer seeked to an
earlier position. Now hr-seek machinery is used to skip at least the
frames that should not be part of playback timeline at all.
demux_mkv: work around bad OutputSamplingFrequency values

Something produces corrupt Matroska files with audio tracks that have
SamplingFrequency set to 44100 and OutputSamplingFrequency to 96000,
when the correct playback rate is 44100. Add a special case for this
44100/96000 combination and override it to 44100/44100; it's unlikely
that anyone would ever want to use this 44100/96000 combination for
real in valid files.
af_volnorm: fix output range with float input

af_volnorm can process either int16_t or float audio data. The float
version used 0 to INT_MAX as full value range, when it should be 0 to
1. This effectively disabled the filter (due to all input being
considered to fall in the silence range). Fix.

Reported by Tobias Jacobi <liquid.acid@gmx.net>.
mixer: keep fractional part of volume setting

mixer_setvolume() accepts float values for volume, but used the
integer function av_clip() to limit range, losing the fractional part
as a side effect. Change the code to use av_clipf() instead. For most
uses this shouldn't make any real difference; actual AO volume
settings may not have that much precision anyway.
configure: cleanup: remove unused xshape switches

They didn't do anything since the internal GUI was removed years ago.
configure: cleanup: remove unused --datadir switch

Unused. mplayer-svn used it as fallback directory to locate the OSD
font, and for the GUI.
configure: remove __builtin_expect check

Change the only usage of HAVE_BUILTIN_EXPECT, demux.h, to use an #ifdef
instead. In theory, a configure check is better, but nobody does it this
way anyway, and we seek to reduce the configure script.
configure: remove check for .align semantics

The check determined whether the argument for .align is in bytes, or
log2(bytes). Apparently it's always in bytes for ELF i386 systems, and
this check is used for x86 inline assembler only. Even if this
assumption should be wrong, it likely won't cause much damage: the
existing code uses it only in the form ".align 4", which means in the
worst case it will try to align to 16 bytes, which doesn't cause any
problems (unless the object file format does not support such a high
alignment).

Update the filters that used this.

Quoting the GNU as manual:

For other systems, including ppc, i386 using a.out format, arm and
strongarm, it is the number of low-order zero bits the location counter
must have after advancement. For example `.align 3' advances the
location counter until it a multiple of 8. If the location counter is
already a multiple of 8, no change is needed.
osdep: remove broken vsscanf() emulation

vsscanf() is in POSIX, C99, mingw, etc. Further, the implementation in
osdep/vsscanf.c was completely broken, and if it worked, it worked only
by chance.
osdep: remove setenv() emulation

mpv doesn't use setenv() anymore. The configure check was actually
removed earlier; maybe it was forgotten to remove this completely.
osdep: remove gettimeofday() emulation

Guaranteed by POSIX, and mingw provides it as well.
windows support: fix _wstat misusage

I have no idea when or how this broke, but _wstati64() is the function
we want anyway (64 bit filesize). Possibly this was a mingw-w64 bug.
It's unknown why "wstat()" just doesn't work in this case, as it's not
defined by MSDN and could be defined by mingw as it needs.
Replace strsep() uses

This function sucks and apparently is not very portable (at least on
mingw, the configure check fails). Also remove the emulation of that
function from osdep/strsep*, and remove the configure check.
configure: remove unused check for mkstemp()

Was used by the win32 loader to implement a similar win32 API function.
configure: remove references to nas
configure: change libcaca test to pkg-config

Caca is important.
Remove netstream support

This allowed to move the input stream layer across the network, allowing
the user to play anything that mplayer could play remotely. For example,
playing a DVD related on a remote server (say, with the host name
"remotehost1") could be done by starting the netstream server on that
remote server, and then running:

    mplayer mpst://remotehost1/dvd://

This would open the DVD on the remote host, and transfer the raw DVD
sector reads over network. It works the same for other protocols, and
all accesses to the stream layer are marshaled over network. It's
comparable to the way the cache layer (--cache) works.

It has questionable use and most likely was barely used at all. There's
lots of potential for breakage, because it doesn't translate the stream
CTRLs to network packets. Just get rid of it.

The server used to be in TOOLS/netstream.c, and was accidentally removed
earlier.