Merge branch 'kk/maint-for-each-ref-multi-sort' into maint-1.7.11

"git for-each-ref" did not honor multiple "--sort=<key>" arguments
correctly.

* kk/maint-for-each-ref-multi-sort:
  for-each-ref: Fix sort with multiple keys
  t6300: test sort with multiple keys

builtin/for-each-ref.c

@@ -962,7 +962,9 @@ static int opt_parse_sort(const struct option *opt, const char *arg, int unset)
 	if (!arg) /* should --no-sort void the list ? */
 		return -1;
 
-	*sort_tail = s = xcalloc(1, sizeof(*s));
+	s = xcalloc(1, sizeof(*s));
+	s->next = *sort_tail;
+	*sort_tail = s;
 
 	if (*arg == '-') {
 		s->reverse = 1;

t/t6300-for-each-ref.sh

@@ -456,4 +456,14 @@ test_atom refs/tags/signed-long contents "subject line
 body contents
 $sig"
 
+cat >expected <<\EOF
+408fe76d02a785a006c2e9c669b7be5589ede96d <committer@example.com> refs/tags/master
+90b5ebede4899eda64893bc2a4c8f1d6fb6dfc40 <committer@example.com> refs/tags/bogo
+EOF
+
+test_expect_success 'Verify sort with multiple keys' '
+	git for-each-ref --format="%(objectname) %(taggeremail) %(refname)" --sort=objectname --sort=taggeremail \
+		refs/tags/bogo refs/tags/master > actual &&
+	test_cmp expected actual
+'
 test_done