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/branch.c

@@ -704,7 +704,10 @@ static int edit_branch_description(const char *branch_name)
 	return 0;
 }
 
-int cmd_branch(int argc, const char **argv, const char *prefix)
+int cmd_branch(int argc,
+	       const char **argv,
+	       const char *prefix,
+	       struct repository *repo UNUSED)
 {
 	/* possible actions */
 	int delete = 0, rename = 0, copy = 0, list = 0,