bug#20677: tooltips generate garbage

[Angelo Graziosi]

After tooltips show up, they do not disappear moving the mouse but leave 
garbage in the Emacs frame.

I see this (on GNU/Linux, GTK build) in recent Emacs master.

This DID NOT happen with the builds I did a few week ago (May 13).

Usually "emacs -Q" is enough to see this issue. It seems a redrawing 
problem because when I click on the upper-right '-' button which reduce 
Emacs to an icon in status bar and then re-enlarging, the garbage 
disappears (but re-appears if the mouse pointer is over an element which 
needs a tooltip).


Ciao,
 Angelo.