disable libtheora, this change leaves all the libtheora related code in svn for now but just disables it in configure
IMO libtheora support should be completely removed but at least under no circumstances must it disable or override our native decoder by default


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@5812 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b