Fixes #673859

Fixes #673859

Conflicts:
	gst/flv/gstflvdemux.c
	gst/matroska/matroska-demux.c

Disable test for smoke elements, which aren't ported yet
(and maybe shouldn't be ported).

Or perhaps it should just be a guint64 channel mask, which would
be nicer in C, but more awkward for bindings (even more so since
we can't add a flags type for it, since that only supports guint
size flags). Fixes wavenc unit test.

https://bugzilla.gnome.org/show_bug.cgi?id=669643

Fixes #673165.

This not really threadsafe in any way.

From 7fda524 to 464fe15

Conflicts:
	gst/matroska/matroska-demux.c
	gst/matroska/matroska-mux.c
	gst/matroska/matroska-read-common.c
	gst/matroska/matroska-read-common.h

Only set DTS on outgoing buffers unless we have a keyframe and then we can set
the PTS to DTS as well.

Conflicts:
	gst/matroska/matroska-demux.c
	gst/matroska/matroska-mux.c
	gst/matroska/matroska-read-common.c
	gst/matroska/matroska-read-common.h