Resolves issue with audio playback where audio playback stops working.

Potential existed for the audio output class to become unsynchronized
with the underlying source data line and attempt to perform a blocking
write to the data line when the data line doesn't have the capacity to
accept the full buffer, and the data line is not started.  Thus,
playback could potentially stay in a persitent blocked state.

Refactored Mono and Stereo audio output implementations to push the
audio buffer queue processing into the parent abstract class.

AudioManager was updated to remove the last time active timestamp out 
of the audio manager and down into the audio output to remove duplicate
timestamp accounting.

src/audio/AudioPacket.java

@@ -64,6 +64,11 @@ public class AudioPacket
 		return mAudioData;
 	}
 	
+	public boolean hasAudioBuffer()
+	{
+		return mAudioData != null;
+	}
+	
 	public enum Type
 	{
 		AUDIO,