interaudiosink: Flush the adapter when we get new caps

Ideally we would drain the source but that would require more coordination
between sink and source than what we currently have.
interaudio: Only flush the ringbuffer on the sink side
interaudiosink: Use the bpf from the audio info instead of hardcoding 4
interaudio: Make buffer size and latency handling more explicit and add properties for them

This now makes audio work more reliable without disconts.
interaudiosrc: Fix compiler warning about unused variables

gstinteraudiosrc.c: In function 'gst_inter_audio_src_create':
gstinteraudiosrc.c:339:27: error: variable 'buffer_samples' set but not used [-Werror=unused-but-set-variable]
   guint64 period_samples, buffer_samples;
                           ^
glimagesink: implement gst_video_overlay_handle_events

https://bugzilla.gnome.org/show_bug.cgi?id=736035
glcontext: fail context creation if glGetString returns NULL
glutils: only attempt getting the app context when we don't already have a display

avoids querying/messaging the world on each frame
h264parse: don't unnecesarily set src_caps

https://bugzilla.gnome.org/show_bug.cgi?id=739374
h265parse: don't unnecesarily set src_caps

https://bugzilla.gnome.org/show_bug.cgi?id=739374
intervideosink: Add some debug output in the render function
intervideosrc: Print a warning into the debug log on generating black frames
glimagesink: clamp the resize width/height to >= 1 to avoid a GL error
vtenc: add realtime and allow-frame-reordering properties
glimagesink: fix possible deadlock on osx

Remove gst_glimage_sink_handle_events call in gst_glimage_sink_init. It was
unnecessary and when the element was instantiated from the main thread, caused a
deadlock in OSX creating the context (thread).
glimagesink: don't make gst_glimage_sink_handle_events call _ensure_gl_setup

gst_glimage_sink_handle_events can be called from the overlay interface and from
the main thread before GL is setup. Before this change, that would call
_ensure_gl_setup() and deadlock on OSX.

Change things so that it's always safe to call gst_glimage_sink_handle_events()
without stuff deadlocking.
smoothstreaming: initialise new GstH264NalUnit fields

CID #1251107.
gstglconfig: Put gstglconfig.h into $(libdir)/gstreamer-1.0/include

It's architecture dependent and should not be placed into the include
directory as the assumption is that all those headers are architecture
independent.

https://bugzilla.gnome.org/show_bug.cgi?id=739767
h265parse: set the HEADER flag on buffers containing VPS, SPS or PPS
h264parse: set the HEADER flag on buffers containing SPS or PPS