bundle: convert to struct object_id

Convert the bundle code, plus the sole external user of struct
ref_list_entry, to use struct object_id.  Include cache.h from within
bundle.h to provide the definition.  Convert some of the hash parsing
code to use parse_oid_hex to avoid needing to hard-code constant values.

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

bundle.h

@@ -1,10 +1,12 @@
 #ifndef BUNDLE_H
 #define BUNDLE_H
 
+#include "cache.h"
+
 struct ref_list {
 	unsigned int nr, alloc;
 	struct ref_list_entry {
-		unsigned char sha1[20];
+		struct object_id oid;
 		char *name;
 	} *list;
 };