Fixes ticket #3181.

Fixes ticket #3184

It was previously int and would return error if decode_coeffs_b()
returns an error; however, that can never happen, so refactor all
that code to make all dependent functions return void also (all the
way up to decode_coeffs_sb()).

The old one didn't use segmentation. One uses segmentation in all frame
types (--aq-mode=1), and the other uses all segmentation features, but
only in inter frames (mbgraph).

This disables backward probability updates, which makes the codec more
friendly for frame-level multi-threading.

For a random 1080p sample, decoding time went from 9.7sec (1 threads)
to 6.0sec (2 threads) and 5.2sec (4 threads) in 2-pass decoding mode.
I don't have any samples that use the parallelmode feature, but the
gains should be higher.

We need more information from last/cur_frame than from reference
buffers, so we can use a simplified structure for reference buffers,
and then store mvs and segmentation map information in last/cur.

They aren't really block-related variables in the sense that they are
not block-coded, rather they are state trackers.

Based on something similar in libav. Author is likely Anton Khirnov
<anton@khirnov.net> but I'm not sure.

Without this nothing will remove it even if it isnt generated in newer
versions anymore.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

Also the libavutil/ffversion.h will be installed.

Rationale:
* Applications might want to know FFmpeg's version besides the individual
  libraries'.
* Avoids file name clash between FFmpeg's ./version.h and lib*/version.h when
  a library source file includes both and is compiled on an out-of-tree build.

Fixes #1769.
Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Reviewed-by: James Almer <jamrial@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

* qatar/master:
  dcadec: Add some logging before returning on error

Conflicts:
	libavcodec/dcadec.c
Merged-by: Michael Niedermayer <michaelni@gmx.at>

* commit 'f058f384':
  configure: Do not use pthread_create to check for pthread
Merged-by: Michael Niedermayer <michaelni@gmx.at>

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

* cigaes/master:
  lavc/srtenc: use bprint for text buffers.
Merged-by: Michael Niedermayer <michaelni@gmx.at>

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

Improve feedback.

Also move FFM section up in the file, and rename it.

Fix trac ticket #3120.

They are only needed by removelogo.
This fixes a link failure in shared builds when compiling with
removelogo disabled but Lavf/SwS enabled
Signed-off-by: James Almer <jamrial@gmail.com>
Reviewed-by: Stefano Sabatini <stefasab@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

Based on a patch by Michael Niedermayer.
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

Certain instrumentation addons leads to a false positive in configure
and link failures at the end of the build phase.
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

* cus/stable:
  ffmpeg: ensure that -fix_sub_duration doesnt create subtitles with zero duration
  ffmpeg: free empty subtitles as well in transcode_subtitles
  ffmpeg: do not pass possibly undefined subtitles to sub2video_update
Merged-by: Michael Niedermayer <michaelni@gmx.at>

* qatar/master:
  go2meeting: disallow tile dimensions that are not multiple of 16
Merged-by: Michael Niedermayer <michaelni@gmx.at>

* commit 'e026ee04':
  mpeg4videodec: move sprite_{shift,traj} from MpegEncContext to Mpeg4DecContext
Merged-by: Michael Niedermayer <michaelni@gmx.at>

* commit '513d849b':
  mpeg4videodec: move num_sprite_warping_points from MpegEncContext to Mpeg4DecContext
Merged-by: Michael Niedermayer <michaelni@gmx.at>

* commit '9ba3fc3e':
  mpeg4videodec: move sprite_brightness_change from MpegEncContext to Mpeg4DecContext
Merged-by: Michael Niedermayer <michaelni@gmx.at>

* commit '58c120a9':
  mpeg4videodec: move scalability from MpegEncContext to Mpeg4DecContext
Merged-by: Michael Niedermayer <michaelni@gmx.at>

* commit '6e81597d':
  mpeg4videodec: move enhancement_type from MpegEncContext to Mpeg4DecContext
Merged-by: Michael Niedermayer <michaelni@gmx.at>

* commit '2992afda':
  mpeg4videodec: remove a write-only variable from MpegEncContext
Merged-by: Michael Niedermayer <michaelni@gmx.at>

* commit '3b1c0f68':
  mpeg4videodec: move new_pred from MpegEncContext to Mpeg4DecContext
Merged-by: Michael Niedermayer <michaelni@gmx.at>

* commit 'e89247de':
  mpeg4videodec: replace MpegEncContext.reduced_res_vop with a local variable
Merged-by: Michael Niedermayer <michaelni@gmx.at>