[DVDPlayer] Take advantage of if evaluation order.
[DVDPlayer] Remove unnecessary NULL check.
changed: Improve/cleanup logging when seeking cached streams
texture: two texture speedups

1. Check to see if we have a texture loaded already before opening/uploading
   another instance of it.

2. Set a time-out for deleting textures. If they are needed again before the
   time-out expires, they are re-added to the loaded textures array and ready
   for use again. Otherwise, they are deleted after X msec. This helps to avoid
   doing _really_ nasty things, like re-loading the background image when
   moving from home to settings.
DllAvCodec.h: remove mention of libavcore that is long gone.
configure: Do not check for libavcore files since it is long gone and xbmc requires ffmpeg 1.0
Remove the checks for AVPacket definitions in libavformat.

It has been moved to libavcodec in 2009, libavcodec version 52, and xbmc requires ffmpeg 1.0, libavcodec version 54, so we can assume AVPacket is always defined in libavcodec.
Drop checks for libav*/opt.h.

It has been moved to libavutil/opt.h in 2010, libavutil versin 50, and xbmc requires ffmpeg 1.0, libavutil version 51.
Remove rgb2rgb.h checks.

This header is unused in xbmc code.
Remove the check for libavutil/mathematics.h and assume it is always present.

This header has existed since years and xbmc will not build with such an old ffmpeg version that does not have it.
Remove the check for libavutil/mem.h and assume it is always present.

This header has existed since 2007 and xbmc will not build with such an old ffmpeg version that does not have it.
Remove the check for libavutil/samplefmt.h and assume it is always present.

This header has existed since libavcore got merged back into libavutil and xbmc will not build with such an old ffmpeg version that does not have it.
Drop support for old ffmpeg header layout.

xbmc requires a ffmpeg version that has the new layout.
configure: remove a no longer valid comment
Restore code parts from [573b4bc18] to improve libav compatibility.
configure: Drop checks for sample_aspect_ratio. They are useless because they are done via #ifery now.
DVDAudioCodecFFmpeg: Make sure swr resampler gets reinited when channel count changes