Fix .po file dependencies to prevent unnecessary rebuilds

- Make convertpofiles depend on $(POFILES) so make checks if .po files
  need to be merged with mailman.pot
- The existing dependency rule %/LC_MESSAGES/mailman.po: mailman.pot
  ensures msgmerge only runs when mailman.pot is newer
- Add --backup=none to msgmerge to avoid creating backup files
- This fixes the issue where .po files were always being merged on
  every make run, even when mailman.pot hadn't changed

Author: jared mauch

messages/Makefile.in

@@ -119,7 +119,9 @@ doinstall: .converted.stamp mofiles
 	../scripts/convert_to_utf8 -d .
 	touch .converted.stamp
 
-convertpofiles: .converted.stamp
+# Ensure .po files are merged with mailman.pot before conversion
+# This depends on the .po files being up to date with mailman.pot
+convertpofiles: $(POFILES) .converted.stamp
 
 mofiles: $(MOFILES)
 
@@ -151,10 +153,11 @@ potfile: marked.files docstring.files
 	(cd ..; $(PROG) -k C_ -p messages -d mailman -D -X messages/marked.files `cat messages/marked.files messages/docstring.files`)
 
 # Update the individual mailman.po files with the new changes to the
-# .pot file
+# .pot file. Make already checks if mailman.pot is newer, but msgmerge -U
+# always updates the file. Use --backup=none to avoid creating backup files.
 %/LC_MESSAGES/mailman.po: mailman.pot
 	@echo "Merging new template file with existing translations"
-	$(MSGMERGE) -U $@ mailman.pot || touch $@
+	@$(MSGMERGE) --update --backup=none $@ mailman.pot || touch $@
 
 
 FORCE: