git-gui: Support 'Visualize All Branches' on Mac OS X.

Now that recent versions of gitk (shipping with at least git 1.5.0-rc1
and later) actually accept command line revision specifiers without
crashing on internal Tk errors we can offer the 'Visualize All Branches'
menu item in the Repository menu on Mac OS X.
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>

git-gui.sh

@@ -3772,12 +3772,10 @@ menu .mbar.repository
 	-label {Visualize Current Branch} \
 	-command {do_gitk {}} \
 	-font font_ui
-if {![is_MacOSX]} {
-	.mbar.repository add command \
-		-label {Visualize All Branches} \
-		-command {do_gitk {--all}} \
-		-font font_ui
-}
+.mbar.repository add command \
+	-label {Visualize All Branches} \
+	-command {do_gitk {--all}} \
+	-font font_ui
 .mbar.repository add separator
 
 if {!$single_commit} {