aggregator: fix locking

We would unlock a mutex we never locked on SEGMENT
events.
videoaggregator: fix broken locking in update_src_caps function

We would unlock an already-unlocked mutex that we never re-locked.

https://bugzilla.gnome.org/show_bug.cgi?id=732750
videoaggregator: Fix some more the locking logic in update_src_caps

We need the GST_OBJECT_LOCK only to iterate the sinkpads, nothing else.

https://bugzilla.gnome.org/show_bug.cgi?id=732750
mpegts: fix leak of language code
mpegts: atsc: fix leak of short name
mpegts: Add padding to public structures

Allows use to add API in the future without breaking ABI. We broke the API/ABI
once between 1.2 and 1.4, let's try to avoid this in the future even if this
is an unstable library.

https://bugzilla.gnome.org/show_bug.cgi?id=730914
mpegts: fix annotation

https://bugzilla.gnome.org/show_bug.cgi?id=730914
mpegts: docs: add missed *_free methods

https://bugzilla.gnome.org/show_bug.cgi?id=730914
mpegts: use getter for egde linkage descriptor type

https://bugzilla.gnome.org/show_bug.cgi?id=730914
mpegts: Fix dvb linkage leaks

CID #1224130
watchdog: Add unit test

And improve some debug prints