gitk: On OSX, bring the gitk window to front

On OSX, Tcl/Tk application windows are created behind all
the applications down the stack of windows.  This is very
annoying, because once a gitk window appears, it's the
downmost window and switching to it is pain.

The patch is: if we are on OSX, use osascript to
bring the current Wish process window to front.

Signed-off-by: Tair Sabirgaliev <tair.sabirgaliev@gmail.com>
Thanks-to: Stefan Haller <lists@haller-berlin.de>
Signed-off-by: Paul Mackerras <paulus@samba.org>

gitk

@@ -11751,6 +11751,15 @@ if {[catch {package require Tk 8.4} err]} {
     exit 1
 }
 
+# on OSX bring the current Wish process window to front
+if {[tk windowingsystem] eq "aqua"} {
+    exec osascript -e [format {
+        tell application "System Events"
+            set frontmost of processes whose unix id is %d to true
+        end tell
+    } [pid] ]
+}
+
 # Unset GIT_TRACE var if set
 if { [info exists ::env(GIT_TRACE)] } {
     unset ::env(GIT_TRACE)