10l (bytes_left() -> url_feof())
10l (updating LRU delta pts for type 1/2 frames)
ensure that checksumming isnt enabled if its not needed
search for next startcode and then search backward to the next valid frame if an inconsistancy is detected
deal with non-frame startcodes in the middle of the stream

Originally committed as revision 2972 to svn://svn.ffmpeg.org/ffmpeg/trunk
