Add *.po target to cannonicalise .po files received from translators.

Makefile

@@ -114,6 +114,11 @@ merge :
 		echo -n msgmerge $(PO)/$$f && $(MSGMERGE) --no-wrap -U $(PO)/$$f $(BUILDDIR)/dnsmasq.pot; \
 	done
 
+# Cannonicalise .po file.
+%.po : 
+	@cd $(BUILDDIR) && $(MAKE) -f $(top)/Makefile dnsmasq.pot
+	mv $(PO)/$*.po $(PO)/$*.po.orig && $(MSGMERGE) --no-wrap $(PO)/$*.po.orig $(BUILDDIR)/dnsmasq.pot >$(PO)/$*.po; 
+
 $(BUILDDIR):
 	mkdir -p $(BUILDDIR)