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.
lavc: export DV profile API used by muxer/demuxer as public
adxdec: get rid of an avpriv function

The only thing the demuxer needs is the sample rate to set the timebase,
which can be simply read with AV_RB32.
oggparsecelt: do not set AVCodecContext.frame_size

It is supposed to be set by decoders only.
mtv: do not set sample_rate for video
mov: free the dv demux context with avformat_free_context()
nsvdec: remove commented out cruft
yuv4mpegenc: do not access AVCodecContext.coded_frame

Its contents are meaningful only if the stream codec context is the one
actually used for encoding, which is often not the case (and is
discouraged).

Use AVCodecContext.field_order instead.
rtpdec: pass an AVFormatContext to ff_parse_fmtp()

Use it for logging, instead of NULL or the stream codec context.