avoid deadlock by synchronizing on addEventProbe (#196)

Author: MaZderMind

src/org/freedesktop/gstreamer/Pad.java

@@ -391,7 +391,7 @@ public void addEventProbe(final EVENT_PROBE listener) {
         addEventProbe(listener, mask);
     }
 
-    void addEventProbe(final EVENT_PROBE listener, final int mask) {
+    synchronized void addEventProbe(final EVENT_PROBE listener, final int mask) {
         final GstPadAPI.PadProbeCallback probe = new GstPadAPI.PadProbeCallback() {
             public PadProbeReturn callback(Pad pad, GstPadProbeInfo probeInfo, Pointer user_data) {
 //        	    System.out.println("CALLBACK " + probeInfo.padProbeType);