ximagesrc: Add missing return value to Buffer dispose function

Depending ont he build, the method could return FALSE, hence never
free the buffers, or already TRUE and lead to a crash:

Fixes: https://bugzilla.gnome.org/show_bug.cgi?id=733695
ximagesrc: Fix warning about missing return value
Makefile: Add usage of build-checks step

Allows building checks without running them
rtph264pay: append profile-level-id to SDP

Append profile-level-id to SDP if available.

https://bugzilla.gnome.org/show_bug.cgi?id=733539
rtph264pay: unbreak au aligned byte-stream payloading
rtspsrc: Push the correct segment in TCP mode when seeking
isomp4/qtmux: Write correct file duration when gaps exist.

When writing out a trak with an edit list, make sure the
overall file duration is also updated to reflect the
lengthening of the stream.

Add some more debug to qtdemux to warn about streams that
are longer than the file and get truncated.
rtph264pay: append packetization mode parameter to SDP

Append packetization-mode parameter to SDP description.
Packetization mode signals the properties of an RTP payload type.

https://bugzilla.gnome.org/show_bug.cgi?id=733556