[Theora] ffmpeg/ffmpeg2theora &vhooks

[j at v2v.cc]

Hi Aphid, 

indeed adding vhook to ffmpeg2theora was easy.
with latest version from svn one can now use vhooks like this:

ffmpeg2theora --vhook '/path/to/watermark.so -f /path/to/overlay.gif' input.dv

it looks like vhooks are broken in ffmpeg cvs right now, but it worked 
with ffmpeg cvs20050918(ubuntu/dapper), i had to copy framehook.h from 
the source to /usr/include/ffmpeg though.

enjoy,
j