Convert find_unique_abbrev* to struct object_id

Convert find_unique_abbrev and find_unique_abbrev_r to each take a
pointer to struct object_id.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/tag.c b/tag.c
index 66210fd..a6e0abc 100644
--- a/tag.c
+++ b/tag.c
@@ -46,7 +46,7 @@ int gpg_verify_tag(const struct object_id *oid, const char *name_to_report,
 		return error("%s: cannot verify a non-tag object of type %s.",
 				name_to_report ?
 				name_to_report :
-				find_unique_abbrev(oid->hash, DEFAULT_ABBREV),
+				find_unique_abbrev(oid, DEFAULT_ABBREV),
 				type_name(type));
 
 	buf = read_sha1_file(oid->hash, &type, &size);
@@ -54,7 +54,7 @@ int gpg_verify_tag(const struct object_id *oid, const char *name_to_report,
 		return error("%s: unable to read file.",
 				name_to_report ?
 				name_to_report :
-				find_unique_abbrev(oid->hash, DEFAULT_ABBREV));
+				find_unique_abbrev(oid, DEFAULT_ABBREV));
 
 	ret = run_gpg_verify(buf, size, flags);