dir.c: make excluded() file scope static

Now there no longer is external callers of this interface, so we can
make it static.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

dir.c

@@ -560,7 +560,7 @@ int excluded_from_list(const char *pathname,
 	return -1; /* undecided */
 }
 
-int excluded(struct dir_struct *dir, const char *pathname, int *dtype_p)
+static int excluded(struct dir_struct *dir, const char *pathname, int *dtype_p)
 {
 	int pathlen = strlen(pathname);
 	int st;