matroskaenc: Allow chapters to be written in trailer

This allows creation of frame accurate chapter marks from sources like
DVD and BD where the precise chapter location is not known until the
chapter mark has been reached during reading.

Signed-off-by: Anton Khirnov <anton@khirnov.net>
Merge remote-tracking branch 'qatar/master'

* qatar/master:
  matroskaenc: Allow chapters to be written in trailer

Conflicts:
	libavformat/matroskaenc.c

Merged-by: Michael Niedermayer <michaelni@gmx.at>
avfilter/vf_yadif: add gbr(a)p support

Suggested-by: durandal_1707
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>