add_packed_ref(): new function in the refs API.

Add a new function add_packed_ref() that adds a reference directly to
the in-memory packed reference cache.  This will be useful for
creating local references while cloning.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs.c

@@ -319,6 +319,12 @@ static struct ref_array *get_packed_refs(struct ref_cache *refs)
 	return &refs->packed;
 }
 
+void add_packed_ref(const char *refname, const unsigned char *sha1)
+{
+	add_ref(get_packed_refs(get_ref_cache(NULL)),
+			create_ref_entry(refname, sha1, REF_ISPACKED, 1));
+}
+
 static void get_ref_dir(struct ref_cache *refs, const char *base,
 			struct ref_array *array)
 {

refs.h

@@ -50,6 +50,12 @@ extern int for_each_rawref(each_ref_fn, void *);
 
 extern void warn_dangling_symref(FILE *fp, const char *msg_fmt, const char *refname);
 
+/*
+ * Add a reference to the in-memory packed reference cache.  To actually
+ * write the reference to the packed-refs file, call pack_refs().
+ */
+extern void add_packed_ref(const char *refname, const unsigned char *sha1);
+
 /*
  * Extra refs will be listed by for_each_ref() before any actual refs
  * for the duration of this process or until clear_extra_refs() is