git: update to v2.5.0

Update to git version v2.5.0.

* Upstream commit 5455ee0573a22bb793a7083d593ae1ace909cd4c (Merge branch
  'bc/object-id') changed API:

  for_each_ref() callback functions were taught to name the objects
  not with "unsigned char sha1[20]" but with "struct object_id".

* Upstream commit dcf692625ac569fefbe52269061230f4fde10e47 (path.c: make
  get_pathname() call sites return const char *)

Signed-off-by: Christian Hesse <mail@eworm.de>

cgit.c

@@ -421,7 +421,7 @@ struct refmatch {
 	int match;
 };
 
-static int find_current_ref(const char *refname, const unsigned char *sha1,
+static int find_current_ref(const char *refname, const struct object_id *oid,
 			    int flags, void *cb_data)
 {
 	struct refmatch *info;