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/merge-recursive.c

@@ -21,7 +21,10 @@ static char *better_branch_name(const char *branch)
 	return xstrdup(name ? name : branch);
 }
 
-int cmd_merge_recursive(int argc, const char **argv, const char *prefix UNUSED)
+int cmd_merge_recursive(int argc,
+			const char **argv,
+			const char *prefix UNUSED,
+			struct repository *repo UNUSED)
 {
 	struct object_id bases[21];
 	unsigned bases_count = 0;