decodebin: unref decode pad after usage

https://bugzilla.gnome.org/show_bug.cgi?id=737757
videoconverter: Free the converter config in free()
decodebin: Free factories array when delaying autoplugging due to non-final caps
decodebin: Only emit the drain signal for the main decode chain, not any subchains

https://bugzilla.gnome.org/show_bug.cgi?id=738064
typefindfunctions: Remove leftover #define from 0.10

https://bugzilla.gnome.org/show_bug.cgi?id=738018
audioresample: remove unused variables

https://bugzilla.gnome.org/show_bug.cgi?id=738026
video-chroma: improve 4x downsampling coefficients
videotestsrc: add gradient pattern

Makes a gradient between background and foreground color.
videoscale: remove FIXME about NV21 support

NV21 is already supported so removing FIXME about adding support for it.
playsink: Use correct property enum value for video-filter property installation
pbutils: Rename clock-base/seqnum-base to timestamp-offset/seqnum-offset

To match how they were renamed elsewhere.
basetextoverlay: Fix segfault when overlay outside the frame

When the textoverlay is set outside the video frame by deltax or deltay the
calculation segfaults, but it is also  unnecessary since it doesn't need to be
displayed. So we should clip the text.

https://bugzilla.gnome.org/show_bug.cgi?id=738242
videoblend: Avoid assigning a negative value to a guint

There are some few but certain conditions where it is possible for the
dest_width to be smaller than x. So we check this before assigning a negative
value to src_width, which is a unsigned and would be promoted to a number that
can segfault videoblend.

https://bugzilla.gnome.org/show_bug.cgi?id=738242
audiodecoder: should post DECODE errors and not ENCODE

Fix error code for audio decoder
audio-channels: allow partially valid channel_mask

Since WAVEFORMATEXTENSIBLE allows to have more channels than
bits in the channel mask we should allow this, too, to avoid
loss of information.

https://bugzilla.gnome.org/show_bug.cgi?id=733405
riff-media: allow more channel_masks

Allow partial valid channel masks.
Set channel mask to 0 for non-valid channel masks.

https://bugzilla.gnome.org/show_bug.cgi?id=733405
tests: parallelise 'make valgrind'

Use $(MAKE) instead of 'make' inside the Makefile,
otherwise the make will run as if -j1 had been
specified and complain about the job server not
being available, and with $(MAKE) in inherits the
parent make's settings it seems.

Upgrade common submodule for parallel check-valgrind.
encodebin: fix some leaks in error code path

Fixes test_encodebin_sink_pads_nopreset_static
running under valgrind.
typefind: use gslice for typefine data

Also use our free function in the failure case.
appsink: Fix gst_app_sink_pull() docs to transfer full for the return value

Also we get a GstSample, not a GstBuffer here.