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/index-pack.c

@@ -1718,7 +1718,10 @@ static void show_pack_info(int stat_only)
 	free(chain_histogram);
 }
 
-int cmd_index_pack(int argc, const char **argv, const char *prefix)
+int cmd_index_pack(int argc,
+		   const char **argv,
+		   const char *prefix,
+		   struct repository *repo UNUSED)
 {
 	int i, fix_thin_pack = 0, verify = 0, stat_only = 0, rev_index;
 	const char *curr_index;