git remote: allow adding remotes agreeing with url.<...>.insteadOf

When adding a remote, we make sure that the remote does not exist
already. However, this test was not quite correct: when the
url.<...>.insteadOf config variable was set to the remote name to be
added, the code would assume that the remote exists already.

Let's allow adding remotes when there is a url.<...>.insteadOf setting
when both the name and the URL agree with the remote to be added.

It might seem like a mistake to compare against remote->url[0] without
verifying that remote->url_nr >=1, but at this point a missing URL has
been filled by the name already, therefore url_nr cannot be zero.

Noticed by Anastas Dancha.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/remote.c

@@ -180,7 +180,9 @@ static int add(int argc, const char **argv)
 	url = argv[1];
 
 	remote = remote_get(name);
-	if (remote && (remote->url_nr > 1 || strcmp(name, remote->url[0]) ||
+	if (remote && (remote->url_nr > 1 ||
+			(strcmp(name, remote->url[0]) &&
+				strcmp(url, remote->url[0])) ||
 			remote->fetch_refspec_nr))
 		die(_("remote %s already exists."), name);