git-gui: Gracefully fall back to po2msg.sh if msgfmt --tcl fails

Mac OS X Tiger may have a msgfmt available but it doesn't understand
how to implement --tcl.  Falling back to po2msg.sh on such systems
is a reasonable behavior.

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

Makefile

@@ -224,6 +224,11 @@ else
 	ifeq ($(shell $(MSGFMT) >/dev/null 2>&1 || echo $$?),127)
 		MSGFMT := $(TCL_PATH) po/po2msg.sh
 	endif
+	ifeq (msgfmt,$(MSGFMT))
+	ifeq ($(shell $(MSGFMT) --tcl -l C -d . /dev/null 2>/dev/null || echo $?),1)
+		MSGFMT := $(TCL_PATH) po/po2msg.sh
+	endif
+	endif
 endif
 
 msgsdir     = $(gg_libdir)/msgs