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/range-diff.c

@@ -13,7 +13,10 @@ N_("git range-diff [<options>] <base> <old-tip> <new-tip>"),
 NULL
 };
 
-int cmd_range_diff(int argc, const char **argv, const char *prefix)
+int cmd_range_diff(int argc,
+		   const char **argv,
+		   const char *prefix,
+		   struct repository *repo UNUSED)
 {
 	struct diff_options diffopt = { NULL };
 	struct strvec other_arg = STRVEC_INIT;