[theora] Indexing Ogg files for faster seeking

[Chris Pearce]

Hey guys,

We've landed keyframe indexing in ffmpeg2theora over the weekend, so if 
you can, please pull ffmpeg2theora from svn and test it. To encode with 
indexing, specify the --seek-index command line parameter when running 
ffmpeg2theora. Please test it, break it, and then report bugs to me, so 
I can improve it!

This uses the "index in skeleton" approach, and writes a Skeleton3.1 
index track when indexing, as per 
http://github.com/cpearce/OggIndex/blob/skeleton-index-per-stream/Index-in-skeleton-spec.txt 
otherwise it writes a Skeleton3.0. It only requires one write pass of 
the main encoded video data.

Firefox index-capable builds are located here:
http://pearce.org.nz/video/try-a87723a3fd1a-linux.tar.bz2
http://pearce.org.nz/video/try-a87723a3fd1a-macosx.dmg
http://pearce.org.nz/video/try-a87723a3fd1a-win32.zip

Chris P.