Makefile: var for documentation files

Makefile

@@ -9,6 +9,7 b' export PREFIX'
 PYTHON=python
 PURE=
 PYFILES:=$(shell find mercurial hgext doc -name '*.py')
+DOCFILES=mercurial/help/*.txt
 
 help:
 	@echo 'Commonly used make targets:'
@@ -85,9 +86,9 b' test-%:'
 
 update-pot: i18n/hg.pot
 
-i18n/hg.pot: $(PYFILES) mercurial/help/*.txt
+i18n/hg.pot: $(PYFILES) $(DOCFILES)
 	$(PYTHON) i18n/hggettext mercurial/commands.py \
-	  hgext/*.py hgext/*/__init__.py mercurial/help/*.txt > i18n/hg.pot
+	  hgext/*.py hgext/*/__init__.py $(DOCFILES) > i18n/hg.pot
         # All strings marked for translation in Mercurial contain
         # ASCII characters only. But some files contain string
         # literals like this '\037\213'. xgettext thinks it has to