git-gui: blame: prevent tool tips from sticking around after Command-Tab

On Mac, tooltips are not automatically removed when a window loses
focus. Furthermore, mouse-move events are only dispatched to the active
window, which means that if we Command-tab to another application while
a tool tip is showing, the tool tip will stay there forever (in front of
other applications). So we must hide it manually when we lose focus.

Do this unconditionally here (i.e. without if {[is_MacOSX]}); it
shouldn't hurt on other platforms, even though they don't seem to have
this problem.

Signed-off-by: Stefan Haller <stefan@haller-berlin.de>
Signed-off-by: Pratyush Yadav <me@yadavpratyush.com>

lib/blame.tcl

@@ -328,6 +328,7 @@ constructor new {i_commit i_path i_jump} {
 		bind $i <Any-Motion>  [cb _show_tooltip $i @%x,%y]
 		bind $i <Any-Enter>   [cb _hide_tooltip]
 		bind $i <Any-Leave>   [cb _hide_tooltip]
+		bind $i <Deactivate>  [cb _hide_tooltip]
 		bind_button3 $i "
 			[cb _hide_tooltip]
 			set cursorX %x