object-store: rename and expand packed_git's sha1 member

This member is used to represent the pack checksum of the pack in
question.  Expand this member to be GIT_MAX_RAWSZ bytes in length so it
works with longer hashes and rename it to be "hash" instead of "sha1".
This transformation was made with a change to the definition and the
following semantic patch:

@@
struct packed_git *E1;
@@
- E1->sha1
+ E1->hash

@@
struct packed_git E1;
@@
- E1.sha1
+ E1.hash

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/pack-redundant.c

@@ -641,7 +641,7 @@ int cmd_pack_redundant(int argc, const char **argv, const char *prefix)
 	pl = red = pack_list_difference(local_packs, min);
 	while (pl) {
 		printf("%s\n%s\n",
-		       sha1_pack_index_name(pl->pack->sha1),
+		       sha1_pack_index_name(pl->pack->hash),
 		       pl->pack->pack_name);
 		pl = pl->next;
 	}