rtspconnection: Add more tests

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=728907
rtspconnection: Empty queue when flush.

Empty the watchs queue when calling
gst_rtsp_watch_set_flushing with flushing variabel is TRUE.

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=728772
rtcpbuffer: check claimed data size against available size

Coverity 1208773
subtitleoverlay: Don't block on non-serialized events

https://bugzilla.gnome.org/show_bug.cgi?id=729321
playsinkconvertbin: Don't block on non-serialized events

https://bugzilla.gnome.org/show_bug.cgi?id=729321
playsink: Don't block on non-serialized events

https://bugzilla.gnome.org/show_bug.cgi?id=729321
playbin: Don't block on non-serialized events

https://bugzilla.gnome.org/show_bug.cgi?id=729321
sdp: Add some more gobject-introspection annotations for bindings

https://bugzilla.gnome.org/show_bug.cgi?id=729123
rtpbasepayload: restrict initial random sequence number to be <= 32767

In order to prevent SRTP roll over counter issues the initial sequence
number is restricted to <= 32767. This is recommended by RFC 4568 section 6.4.
videodecoder: do not parse caps for not using it

Saving some cpu
rtpbuffer: avoid underflow in size calculation
rtspdefs: remove outdated comments
rtpbasepayload: Save the PT after fixating
Automatic update of common submodule

From bcb1518 to 211fa5f
tests/check/libs/rtpbasepayload.c: Run gst-indent

https://bugzilla.gnome.org/show_bug.cgi?id=725361
rtpbasepayload: Implement reconfigure event & renegotiation without subclass

Implement the reconfigure event, also do correct downstream caps negotiation
if the subclass doesn't implementy set_caps.

https://bugzilla.gnome.org/show_bug.cgi?id=725361
po: Update translations
Update .po files
Release 1.3.1
textoverlay: Link unit test with the local version of the library, not an installed one