configure: msvc: Set the target windows version to XP if no target is set

MSVC 2010 (or more precisely, Windows SDK 7.0 which comes with MSVC
2010) sets _WIN32_WINNT to the constant for Windows 7 if nothing is
set. This could lead to the libav configure script detecting and
using functions only present in Windows 7 or newer, which in most
cases isn't desired. If the caller explicitly wants this, the caller
can add the _WIN32_WINNT define via --extra-cflags, setting the desired
version.

Signed-off-by: Martin Storsjö <martin@martin.st>
win32: Do not use GetProcAddress when compiled for Vista+

Instead link directly to the condition variable functions.

Signed-off-by: Martin Storsjö <martin@martin.st>
vorbis: refactor vorbis_residue_decode_internal
vorbis: use normal integer values for iterators

No need to use fixed-size integers.
vorbis: simplify the inner loop in setup_classifs
vorbis: fallback to normal division instead of crashing

The use of ff_inverse speeds up slightly arches + compilers that
do not provide a division faster than the whole machinery, such
as ppc32 + gcc4.7, but has operational limits.

Drop the always-enable assert and provide a fallback.
mpegvideo: unref old current_picture before allocating a new one

Allows decoding with only three frame buffers with frame reference
counting. Fixes VAAPI based decoding in vlc which uses only three
frame buffers for the mpegvideo-based codecs.
Merge commit '0b6899f154347cdd0aa66c5ec16ed9c65871766f'

* commit '0b6899f154347cdd0aa66c5ec16ed9c65871766f':
  configure: msvc: Set the target windows version to XP if no target is set

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit 'c360fb174b01170ab3fd3048d4d0acb44aa4e834'

* commit 'c360fb174b01170ab3fd3048d4d0acb44aa4e834':
  win32: Do not use GetProcAddress when compiled for Vista+

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit '98186578a2a21af5bfe6dd71d222dc270f763c7d'

* commit '98186578a2a21af5bfe6dd71d222dc270f763c7d':
  vorbis: refactor vorbis_residue_decode_internal

Conflicts:
	libavcodec/vorbisdec.c

Merged-by: Michael Niedermayer <michaelni@gmx.at>
doc/filters: extend/fix documentation for the geq filter
doc/filters: add RGB geq example
Merge commit '36f10380043c8b8c5cbf8c1add8695089cdaa341'

* commit '36f10380043c8b8c5cbf8c1add8695089cdaa341':
  vorbis: use normal integer values for iterators

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit 'ddf1b4a2f8a680126eb611428e4f47e6e5b8c6c0'

* commit 'ddf1b4a2f8a680126eb611428e4f47e6e5b8c6c0':
  vorbis: simplify the inner loop in setup_classifs

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit 'db347280eb3746d7b70888db97f1efe5f06f5624'

* commit 'db347280eb3746d7b70888db97f1efe5f06f5624':
  vorbis: fallback to normal division instead of crashing

Conflicts:
	libavcodec/vorbisdec.c

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge remote-tracking branch 'qatar/master'

* qatar/master:
  mpegvideo: unref old current_picture before allocating a new one

Merged-by: Michael Niedermayer <michaelni@gmx.at>
avutil/hmac: silence pointer type warnings

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/ratecontrol: silence "warning: expected_bits may be used uninitialized in this function"
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
lavd/v4l2enc: check write return value.
libx264: silence: warning: the address of val will always evaluate as true

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>