fsck: reject .gitmodules git:// urls with newlines

The previous commit taught the clone/fetch client side to reject a
git:// URL with a newline in it. Let's also catch these when fscking a
.gitmodules file, which will give an earlier warning.

Note that it would be simpler to just complain about newline in _any_
URL, but an earlier tightening for http/ftp made sure we kept allowing
newlines for unknown protocols (and this is covered in the tests). So
we'll stick to that precedent.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

fsck.c

@@ -1086,7 +1086,7 @@ static int check_submodule_url(const char *url)
 	if (looks_like_command_line_option(url))
 		return -1;
 
-	if (submodule_url_is_relative(url)) {
+	if (submodule_url_is_relative(url) || starts_with(url, "git://")) {
 		char *decoded;
 		const char *next;
 		int has_nl;