What steps will reproduce the problem?
1. Click the window client area
2. MouseOverEvents are reported in addition to the button event
3. Adding EnterWindowMask | EnterWindowMask to GLX Surface's subwindow's
Xlib event mask shows EnterNotify and LeaveNotify to the subwindow
4. Commenting XMapWindow from the Surface constructor gets rid of the extra
Enter/LeaveNotify events

What is the expected output? What do you see instead?
Expected output:
ButtonEvent(x = 138, y = 147, button = Left, state = Down, buttons = None ,
keymod = None )
ButtonEvent(x = 138, y = 147, button = Left, state = Up, buttons = Left ,
keymod = None )


MouseOverEvent(x = 195, y = 167, inside = Inside)
MouseOverEvent(x = 195, y = 167, inside = Outside)
ButtonEvent(x = 195, y = 167, button = Left, state = Down, buttons = None ,
keymod = None )
MouseOverEvent(x = 195, y = 167, inside = Inside)
ButtonEvent(x = 195, y = 167, button = Left, state = Up, buttons = Left ,
keymod = None )
MouseOverEvent(x = 195, y = 167, inside = Outside)

Mercurial revision: be3c3cf162ef