Merge remote-tracking branch 'qatar/master'

* qatar/master:
  avconv: use different variables for decoded and filtered frame.
  avconv: add support for copying attachments.
  matroskaenc: write attachments.
  matroskadec: export mimetype of attachments as metadata.
  avconv: factorize common code from new_*_stream()
  doc/avconv: expand documentation for some options.
  doc/avconv: document -timelimit.

Conflicts:
	avconv.c
	cmdutils.c
	tests/codec-regression.sh

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