ref-filter: resurrect "strip" as a synonym to "lstrip"

We forgot that "strip" was introduced at 0571979bd6 ("tag: do not
show ambiguous tag names as "tags/foo"", 2016-01-25) as part of Git
2.8 (and 2.7.1) when we started calling this "lstrip" to make it
easier to explain the new "rstrip" operation.

We shouldn't have renamed the existing one; "lstrip" should have
been a new synonym that means the same thing as "strip".  Scripts
in the wild are surely using the original form already.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/ref-filter.c b/ref-filter.c
index 01b5c18..2a94d6d 100644
--- a/ref-filter.c
+++ b/ref-filter.c
@@ -112,7 +112,8 @@ static void refname_atom_parser_internal(struct refname_atom *atom,
 		atom->option = R_NORMAL;
 	else if (!strcmp(arg, "short"))
 		atom->option = R_SHORT;
-	else if (skip_prefix(arg, "lstrip=", &arg)) {
+	else if (skip_prefix(arg, "lstrip=", &arg) ||
+		 skip_prefix(arg, "strip=", &arg)) {
 		atom->option = R_LSTRIP;
 		if (strtol_i(arg, 10, &atom->lstrip))
 			die(_("Integer value expected refname:lstrip=%s"), arg);