po4a/update-po: Display the script name consistently in error messages.

po4a/update-po

@@ -26,7 +26,7 @@ fi
 if test ! -f po4a.conf; then
 	cd `dirname "$0"` || exit 1
 	if test ! -f po4a.conf; then
-		echo "update-po: Error: Cannot find po4a.conf." >&2
+		echo "po4a/update-po: Error: Cannot find po4a.conf." >&2
 		exit 1
 	fi
 fi