cdg: set the keyframe flag on the first packet

Bug-Id: 55
avformat: update muxing doxy

The callers should now set the stream timebase, not the codec one.
avconv: set the output stream timebase

This is required by the new API.
Merge commit 'abda15a990527557c20848f6ca2f82eb85e76dc9'

* commit 'abda15a990527557c20848f6ca2f82eb85e76dc9':
  cdg: set the keyframe flag on the first packet

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit 'c9c1265c52910578d3db1a6205c85b91ead0903f'

* commit 'c9c1265c52910578d3db1a6205c85b91ead0903f':
  avformat: update muxing doxy

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit '3f3232a371cc88696184d9aef1f812656264e56c'

* commit '3f3232a371cc88696184d9aef1f812656264e56c':
  avconv: set the output stream timebase

Conflicts:
	ffmpeg.c

Merged-by: Michael Niedermayer <michaelni@gmx.at>
ffmpeg: remove common factors from copied timebase

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>