sha1_file: make packed_object_info public

Some code may have a pack/offset pair for an object, but
would like to look up more information. Using
sha1_object_info() is too heavy-weight; it starts from the
sha1 and has to find the pack again (so not only does it waste
time, it might not even find the same instance).

In some cases, this problem is solved by helpers like
get_size_from_delta(), which is used by pack-objects to take
a shortcut for objects whose packed representation has
already been found. But there's no similar function for
getting the object type, for instance. Rather than introduce
one, let's just make the whole packed_object_info() available.
It is smart enough to spend effort only on the items the
caller wants.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

cache.h

@@ -1550,6 +1550,7 @@ struct object_info {
 #define OBJECT_INFO_INIT {NULL}
 
 extern int sha1_object_info_extended(const unsigned char *, struct object_info *, unsigned flags);
+extern int packed_object_info(struct packed_git *pack, off_t offset, struct object_info *);
 
 /* Dumb servers support */
 extern int update_server_info(int);

sha1_file.c

@@ -1970,8 +1970,8 @@ static enum object_type packed_to_object_type(struct packed_git *p,
 	goto out;
 }
 
-static int packed_object_info(struct packed_git *p, off_t obj_offset,
-			      struct object_info *oi)
+int packed_object_info(struct packed_git *p, off_t obj_offset,
+		       struct object_info *oi)
 {
 	struct pack_window *w_curs = NULL;
 	unsigned long size;