git-gui: Don't delete send on Windows as it doesn't exist

The Windows port of Tk does not have the send command so we
cannot delete it from our global namespace, but the Mac OS
X and X11 ports do have it.  Switching this delete attempt
into a catch makes send go away, or stay away.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

git-gui.sh

@@ -42,7 +42,7 @@ if {[catch {package require Tcl 8.4} err]
 	exit 1
 }
 
-rename send {} ; # What an evil concept...
+catch {rename send {}} ; # What an evil concept...
 
 ######################################################################
 ##