waylandsink/wlwindow: do not commit a resize when it happens due to a video info change

1) We know that gst_wayland_sink_render() will commit the surface
   in the same thread a little later, as gst_wl_window_set_video_info()
   is always called from there, so we can save the compositor from
   some extra calculations.
2) We should not commit a resize with the new video info while we are still
   showing the buffer of the previous video, with the old caps, as that
   would probably be a visible resize glitch.
wayland: install .pc file
waylandsink: remove the buffer from the surface when going PAUSED -> READY

This essentially hides the video and allows the application to
potentially draw a black background or whatever else it wants.
This allows to differentiate the "paused" and "stopped" modes
from the user's point of view.

Also reworded a comment there to make my thinking more clear,
since the "reason for keeping the display around" is not really
the exposed() calls, as there is no buffer shown in READY/NULL
anymore.
waylandsink/wldisplay: verify that all the required interfaces have been found on the compositor

This allows waylandsink to fail gracefully before going to READY
in case one of the required interfaces does not exist. Not all
interfaces are necessary for all modes of operation, but it is
better imho to fail before going to READY if at least one feature
is not supported, than to fail and/or crash at some later point.

In the future we may want to relax this restriction and allow certain
interfaces not to be present under certain circumstances, for example
if there is an alternative similar interface available (for instance,
xdg_shell instead of wl_shell), but for now let's require them all.
Weston supports them all, which is enough for us now. Other compositors
should really implement them if they don't already. I don't like the
idea of supporting many different compositors with different sets of
interfaces implemented. wl_subcompositor, wl_shm and wl_scaler are
really essential for having a nice video sink. Enough said.
gst-libs: fix uninstalled build of new wayland lib
wayland: add unstable API guards to wayland library header
pnmdec: Added PBM Support

https://bugzilla.gnome.org/show_bug.cgi?id=730523
win32: update exports for changed h264 codec parser API
glfiltershader: port to GLES2

Provide a time variable
glframebuffer: don't segfault needlessly with GLES2

gst_gl_framebuffer_use_v2 was using a function that is not available
with GLES2
pnm: link against libgstbase for GstAdapter

https://bugzilla.gnome.org/show_bug.cgi?id=730523
opengl: add element for transforming video geometry

* add graphene as soft dependency for linear algebra
gstsrtpenc: add allow-repeat-tx property
srtpenc: improve property comments

Add a Note to the allow-repeat-tx property because it is potentially
insecure when used incorrectly.

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=731714
gstsrtpenc: unref event when needed

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=731768
hlsdemux: Directly convert GErrors to error messages

This will make sure that we don't leak debug information into the actual
error message string and keep it behind the debug string.
hlsdemux: Propagate error messages from the source element up in the hierarchy

Instead of inventing our own generic error strings which are mostly useless.
hlsdemux: Include a more descriptive error message
hlsdemux: Include the debug string in the error messages we propagate from the
source
uridownloader: Include the debug string in the error messages we propagate from t source