cache: convert struct cache_entry to use struct object_id

Convert struct cache_entry to use struct object_id by applying the
following semantic patch and the object_id transforms from contrib, plus
the actual change to the struct:

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

@@
struct cache_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>

builtin/read-tree.c

@@ -78,7 +78,7 @@ static void debug_stage(const char *label, const struct cache_entry *ce,
 	else
 		printf("%06o #%d %s %.8s\n",
 		       ce->ce_mode, ce_stage(ce), ce->name,
-		       sha1_to_hex(ce->sha1));
+		       oid_to_hex(&ce->oid));
 }
 
 static int debug_merge(const struct cache_entry * const *stages,