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/fetch.c

@@ -2138,7 +2138,10 @@ static int fetch_one(struct remote *remote, int argc, const char **argv,
 	return exit_code;
 }
 
-int cmd_fetch(int argc, const char **argv, const char *prefix)
+int cmd_fetch(int argc,
+	      const char **argv,
+	      const char *prefix,
+	      struct repository *repo UNUSED)
 {
 	struct fetch_config config = {
 		.display_format = DISPLAY_FORMAT_FULL,