Changed a bunch of calls to sprintf to snprintf to protect against buffer

overflows.

Fix streaming from non-streaming ffm files. It turned out that you
always got 'index & id do not match' errors.

Add some more error detection on getting FFM feeds


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@2523 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b