devdraw: fix mouse(3) moveto on OS X

R=rsc
CC=codebot
http://codereview.appspot.com/224104

src/cmd/devdraw/osx-screen-carbon.m

@@ -423,6 +423,12 @@ _screeninit(void)
 	if(multitouch)
 		InitMultiTouch();
 
+	// CoreGraphics pins mouse events to the destination point of a
+	// CGWarpMouseCursorPosition (see setmouse) for an interval of time
+	// following the move. Disable this by setting the interval to zero
+	// seconds.
+	CGSetLocalEventsSuppressionInterval(0.0);
+
 	InitCursor();
 }