pack: convert struct pack_idx_entry to struct object_id

Convert struct pack_idx_entry to use struct object_id by changing the
definition and applying the following semantic patch, plus the standard
object_id transforms:

@@
struct pack_idx_entry E1;
@@
- E1.sha1
+ E1.oid.hash

@@
struct pack_idx_entry *E1;
@@
- E1->sha1
+ E1->oid.hash

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

pack.h

@@ -67,7 +67,7 @@ struct pack_idx_header {
  * Common part of object structure used for write_idx_file
  */
 struct pack_idx_entry {
-	unsigned char sha1[20];
+	struct object_id oid;
 	uint32_t crc32;
 	off_t offset;
 };