git-gui: Exit shortcut in MacOSX repaired

Now, as in all OSX apps, there is only one quit menu entry.
It's automatically in the wish menu and calls ::tk::mac::Quit when used.

Signed-off-by: Soeren Finster <sf@9by6.de>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

git-gui.sh

@@ -1995,9 +1995,13 @@ if {[is_enabled multicommit]} {
 	}
 }
 
+if {[is_MacOSX]} {
+	proc ::tk::mac::Quit {args} { do_quit }
+} else {
 	.mbar.repository add command -label [mc Quit] \
 		-command do_quit \
 		-accelerator $M1T-Q
+}
 
 # -- Edit Menu
 #