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/ls-files.c

@@ -561,7 +561,10 @@ static int option_parse_exclude_standard(const struct option *opt,
 	return 0;
 }
 
-int cmd_ls_files(int argc, const char **argv, const char *cmd_prefix)
+int cmd_ls_files(int argc,
+		 const char **argv,
+		 const char *cmd_prefix,
+		 struct repository *repo UNUSED)
 {
 	int require_work_tree = 0, show_tag = 0, i;
 	char *max_prefix;