Set keyframe flag only on IDR-frames (needed for reordering across I-frames).

Read vui bitstream restrictions (allows B-frame delay in advance, rather than waiting till we're out of order.)
Mark duplicate frames due to delay as duplicates.


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@4028 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b