gitk: Default to using po2msg.sh if msgfmt doesn't grok --tcl, -l and -d

This is a similar change to that submitted by Junio C Hamano for
git-gui.  It tests whether the msgfmt command can be run successfully
with --tcl, -l and -d, and if not, falls back to using po/po2msg.sh.

Signed-off-by: Paul Mackerras <paulus@samba.org>

Makefile

@@ -8,6 +8,7 @@ gitk_libdir   ?= $(sharedir)/gitk/lib
 msgsdir    ?= $(gitk_libdir)/msgs
 msgsdir_SQ  = $(subst ','\'',$(msgsdir))
 
+TCL_PATH ?= tclsh
 TCLTK_PATH ?= wish
 INSTALL ?= install
 RM ?= rm -f
@@ -22,6 +23,9 @@ ifdef NO_MSGFMT
 	MSGFMT ?= $(TCL_PATH) po/po2msg.sh
 else
 	MSGFMT ?= msgfmt
+	ifneq ($(shell $(MSGFMT) --tcl -l C -d . /dev/null 2>/dev/null; echo $$?),0)
+		MSGFMT := $(TCL_PATH) po/po2msg.sh
+	endif
 endif
 
 PO_TEMPLATE = po/gitk.pot