shallow: add repository argument to is_repository_shallow

Add a repository argument to allow callers of is_repository_shallow
to be more specific about which repository to handle. This is a small
mechanical change; it doesn't change the implementation to handle
repositories other than the_repository yet.

As with the previous commits, use a macro to catch callers passing a
repository other than the_repository at compile time.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/fetch.c b/builtin/fetch.c
index c1f2df9..5514067 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -1445,7 +1445,7 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 	if (unshallow) {
 		if (depth)
 			die(_("--depth and --unshallow cannot be used together"));
-		else if (!is_repository_shallow())
+		else if (!is_repository_shallow(the_repository))
 			die(_("--unshallow on a complete repository does not make sense"));
 		else
 			depth = xstrfmt("%d", INFINITE_DEPTH);