add update-po shortcut.

Makefile.am

@@ -1,5 +1,7 @@
 AUTOMAKE_OPTIONS = 1.9.7
 
+LOCALES = ja
+
 AM_CPPFLAGS = $(MYSQL_INC) $(GROONGA_CFLAGS) $(MYSQL_VERSION_CFLAGS)
 ACLOCAL_AMFLAGS = $$ACLOCAL_ARGS
 
@@ -61,6 +63,11 @@ update-latest-release:
 	  packages/rpm/centos/mysql-groonga.spec.in		\
 	  packages/debian/changelog
 
+update-po:
+	@for lang in $(LOCALES); do						\
+	  (cd $(top_srcdir)/doc/locale/$$lang/LC_MESSAGES && make update)	\
+	done
+
 update-document:
 	@if test -z "$(MROONGA_GITHUB_COM_PATH)"; then			\
 	  echo "\$$(MROONGA_GITHUB_COM_PATH) is missing";		\