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