Work around gcc 4.0.3 bug.

This appears to fix the sim-eng build on the gDapper build machines.

Basic problem is that LayerBuffer::OverlaySource has a constructor that
calls SurfaceFlinger.signalEvent().  SurfaceFlinger lists LayerBuffer
as a friend, but that's not enough to convince gcc that the embedded
OverlaySource class is also a friend.  I don't see a way to make them
friendly, so I marked signalEvent() as public.

libs/surfaceflinger/SurfaceFlinger.h

@@ -250,7 +250,9 @@ private:
           GraphicPlane&     graphicPlane(int dpy);
 
             void        waitForEvent();
+public:     // hack to work around gcc 4.0.3 bug
             void        signalEvent();
+private:
             void        signalDelayedEvent(nsecs_t delay);
 
             void        handleConsoleEvents();