fixes the random dts/pts during encoding
asf preroll fix
no more initial zero frames for b frame encoding
mpeg-es dts during demuxing fixed
.ffm timestamp scale fixed, ffm is still broken though


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@3168 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b