builtin: add a repository parameter for builtin functions

In order to reduce the usage of the global the_repository, add a
parameter to builtin functions that will get passed a repository
variable.

This commit uses UNUSED on most of the builtin functions, as subsequent
commits will modify the actual builtins to pass the repository parameter
down.

Signed-off-by: John Cai <johncai86@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/multi-pack-index.c

@@ -267,8 +267,10 @@ static int cmd_multi_pack_index_repack(int argc, const char **argv,
 			   (size_t)opts.batch_size, opts.flags);
 }
 
-int cmd_multi_pack_index(int argc, const char **argv,
-			 const char *prefix)
+int cmd_multi_pack_index(int argc,
+			 const char **argv,
+			 const char *prefix,
+			 struct repository *repo UNUSED)
 {
 	int res;
 	parse_opt_subcommand_fn *fn = NULL;