h264: make context_count unsigned

Removes the bogus but scary looking warning 'libavcodec/h264.c:4529:49:
warning: array subscript is below array bounds [-Warray-bounds]'.
jv: detect partial packets in the demuxer

Fixes fate-jv under valgrind which reports a different CRC for the last
frame from a partial read.
configure: avserver does not need $ldl

Loadable plugins were removed in d010e95f86089abe9a3d4d4a66ac8102312d28a4.
configure: do not link libraries against program-specific dependencies

Bug-Id: 635
mpeg12dec: do not add stereo3D side data to a non-existing frame

User data is usually coded before slice data. That means the frame
the user data belongs to is not available while parsing the user data.
The stereo3D side data has to use the same indirection over the private
context as pan scan information and A53 captions.

Bug-Id:632
h264: Refactor ff_h264_decode_ref_pic_list_reordering

In preparation for MVC support.
h264: print values in case of error

Also make error style consistent and drop redundant information.
h264: store current_sps_id inside the current sps

In preparation for MVC support.
h264: drop outdated comments
h264_sei: name buffering period type consistently
h264_sei: reorder headers

Also drop unused assert.h.
Doxyfile: Only set HTML_{HEADER|FOOTER|STYLESHEET} from doxy_wrapper.sh
build: Do not pass HTML snippets and stylesheet as input to Doxygen

These files are referenced elsewhere and only generate warnings if
presented to Doxygen as input files.
doxygen: Set EXAMPLE_PATH from within doxy-wrapper.sh

This allows using the libav source path as the example path.
build: doxy: Include code examples in Doxygen documentation
doc/examples: misc Doxygen markup improvements

Add properly formatted @example tag and fix Doxygen syntax.
libx265: Fix use of uninitialized input picture

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
libx265: Remove redundant default param call

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
utvideoenc: Enable support for multiple slices and use them

The official Ut Video decoder only threads with slices, thus until
now any files encoded by the libavcodec encoder have only been
decodable with a single thread. The default slice count is now
set to subsampled_height / 120.

Also sets slices to 1 for the Ut Video encoder tests to keep them
green.

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
ppc: reduce overreads when loading 8 pixels in altivec dsp functions

Altivec can only load naturally aligned vectors. To handle possibly
unaligned data a second vector is loaded from an offset of the original
location and the data is recovered through a vector permutation.
Overreads are minimal if the offset for second load points to the last
element of data. This is 7 for loading eight 8-bit pixels and overreads
are reduced from 16 bytes to 8 bytes if the pixels are 64-bit aligned.
For unaligned pixels the overread is reduced from 23 bytes to 15 bytes
in the worst case.