dsputil: Move apply_window_int16 to ac3dsp

The (optimized) functions are used nowhere else.
configure: Move adding of compat objects out of libc detection
avformat: AviSynth demuxer rewrite

Directly loads AviSynth through LoadLibrary instead of relying on
Video for Windows, and supports using AvxSynth (via dlopen) to
open scripts on Linux and OS X.

Error messages from AviSynth/AvxSynth are now reported through
av_log and exit, rather than the traditional behavior of generating
an error video that the user would need to watch to diagnose.

The main rewrite was authored by d s <avxsynth.testing@gmail.com>
from the AvxSynth team, with additional contributions by

Oka Motofumi <chikuzen.mo@gmail.com>
Stephen Hutchinson <qyot27@gmail.com>
Diego Biurrun <diego@biurrun.de>
Anton Khirnov <anton@khirnov.net>

Signed-off-by: Anton Khirnov <anton@khirnov.net>
Merge commit '4958f35a2ebc307049ff2104ffb944f5f457feb3'

* commit '4958f35a2ebc307049ff2104ffb944f5f457feb3':
  dsputil: Move apply_window_int16 to ac3dsp

Conflicts:
	libavcodec/arm/ac3dsp_init_arm.c
	libavcodec/arm/ac3dsp_neon.S
	libavcodec/x86/ac3dsp_init.c

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

* qatar/master:
  configure: Move adding of compat objects out of libc detection

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit 'f0b234ab9e406efee85c17eb435db646092a943b'

* commit 'f0b234ab9e406efee85c17eb435db646092a943b':
  avformat: AviSynth demuxer rewrite

Conflicts:
	configure
	libavformat/avisynth.c

See: b9ad009475f3afb76bd2fbd92936dc4d4cd441ec (as well as later commits)
Merged-by: Michael Niedermayer <michaelni@gmx.at>
Add support for picture_ptr field in MJpegDecodeContext

Signed-off-by: Anton Khirnov <anton@khirnov.net>
(cherry picked from commit e0e3b8b297bae5144f23fd4b46a1309857040b63)

Conflicts:

	libavcodec/jpeglsdec.c
	libavcodec/mjpegbdec.c
	libavcodec/mjpegdec.c

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