GraphUI: Fix using multiple texture units w/ opt. colorTexUnit in GLRegion

The texture unit has to be updated always,
since program maybe used by multiple regions and diff. texUnits
GLMediaPlayer: Fix video stutter if using NullAudioSink

NullAudioSink shall return the last enqueued PTS in getPTS()
not causing a-v delta measure based on lagging audio in player.
Remove explicit xcode.clang property files
Bug 1011 / Bug 1012: GLMediaPlayer Audio/Video stuttering w/ OSX and OpenAL/JOAL (works using openal-soft default on all platforms now)
Graph: Fix GLSL issue w/ ES3, add 'const float sample_count', since define SAMPLE_COUNT is of type 'int'