wavenc: generate a non-empty data header

Restore the behavior of the element to the state before commit
db29522a430e44450415ca3676abd1b77ee923d9. A non-empty header is
generated and when the EOS event is received the header is generated
again, this time with the correct size.

https://bugzilla.gnome.org/show_bug.cgi?id=711699
matroskademux: Avoid division by zero assert in gst_matroska_demux_search_pos

https://bugzilla.gnome.org/show_bug.cgi?id=711829
rtpjitterbuffer: fix crash when do-retransmission=true and a lot of buffers are lost

The problem here was that the jitterbuffer lock was unlocked to push
the event, but that caused another thread to remove the timer currently
being processed, probably because the amount of rtx events
(and therefore timers) was getting too high. The solution is to
unlock and push the event only after timer processing has finished.

fixes https://bugzilla.gnome.org/show_bug.cgi?id=711131
ac3parse: correctly handle timestamps when parsing x-private1-ac3

... the way it has always worked fine in a52dec.
check: add rtpsession test

Add a basic rtpsession test to ensure that RR blocks are generated when
multiple SSRC senders are active.

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=711270
gstrtpsession: send custom upstream event "GstRTPCollision" on send_rtp_sink pad

See https://bugzilla.gnome.org/show_bug.cgi?id=711560
rtpsession: remove collision reconfigure event

Remove bogus reconfigure event on collision, we don't want to send the event on
the receiving RTP pad and the collision event is now handling this
case.

See https://bugzilla.gnome.org/show_bug.cgi?id=711560
v4l2: init v4l2_buffer to 0x0 before ioctl

https://bugzilla.gnome.org/show_bug.cgi?id=712137
rtspsrc: Use the synced buffer mode in auto mode if a clock provider is in the SDP
gstpay: only send one caps

Only send one caps in a packet. Two caps can happen when setcaps is called and
the config-interval expires at the same time.
jitterbuffer: advance expected seqnum after dropping

After dropping a buffer, move our expected seqnum

Conflicts:
	gst/rtpmanager/gstrtpjitterbuffer.c
v4l2object: print FOURCC_FORMAT when enumerating

https://bugzilla.gnome.org/show_bug.cgi?id=712206
rtpjitterbuffer: implement rtx statistics
rtpjitterbuffer: rename property to 'stats'

This makes the unit test work.
We can later also add more stats, not specific to retransmission.

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=711411
qtmux: fix playback regression

In ae1150e85cf99d7482933aa6f7e4f012fe45a3ec flipping a condition misaligned the
else branch, where for there condition that was change there is none.
Fixes #712303
qtdemux: remove math operation from loop

The elst_offset doesn't change inside the loop, so compute it
outside
gstrtpsession: Implement a number of feedback packet statistics

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=711693
rtpjitterbuffer: Fix stats property field names and documentation
ximagesrc: Remove buffer pool

The pool was intended to optimize dynamic image sizes, which was never
implemented. when the images size actually changes the buffers resources
are free'd by gst_ximageutil_ximage_destroy before it's refcount has hit
zero, resulting in image corruption or segfaults.

This should be reimplemented in ximageutil.c as a GstBufferPool owned by
xcontext.
ximagesrc: Add Xcomposite configure and runtime checks