initialize the _shouldLoopbackForAgent variable
Merge pull request #259 from birarda/mixer-crash

fix the audio-mixer crash for uninitialized _shouldLoopbackForAgent variable
make sure that the AudioRingBuffer exists before trying to use it
Merge pull request #260 from birarda/mixer-crash

more fixes for audio mixer crashing:
cleaned up avatar slow-down upon nearness; fixed mouse pressed bug;
Merge remote-tracking branch 'upstream/master'