refs: add a "for_each_replace_ref" function

This is some preparation work for the following patches that are using
the "refs/replace/" ref namespace.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs.c

@@ -667,6 +667,11 @@ int for_each_remote_ref(each_ref_fn fn, void *cb_data)
 	return for_each_ref_in("refs/remotes/", fn, cb_data);
 }
 
+int for_each_replace_ref(each_ref_fn fn, void *cb_data)
+{
+	return do_for_each_ref("refs/replace/", fn, 13, 0, cb_data);
+}
+
 int for_each_rawref(each_ref_fn fn, void *cb_data)
 {
 	return do_for_each_ref("refs/", fn, 0,

refs.h

@@ -24,6 +24,7 @@ extern int for_each_ref_in(const char *, each_ref_fn, void *);
 extern int for_each_tag_ref(each_ref_fn, void *);
 extern int for_each_branch_ref(each_ref_fn, void *);
 extern int for_each_remote_ref(each_ref_fn, void *);
+extern int for_each_replace_ref(each_ref_fn, void *);
 
 /* can be used to learn about broken ref and symref */
 extern int for_each_rawref(each_ref_fn, void *);