Fix remote.<remote>.vcs

remote.<remote>.vcs causes remote->foreign_vcs to be set on entry to
transport_get(). Unfortunately, the code assumed that any such entry
is stale from previous round.

Fix this by making VCS set by URL to be volatile w.r.t. transport_get()
instead.

Signed-off-by: Ilari Liusvaara <ilari.liusvaara@elisanet.fi>
Acked-by: Daniel Barkalow <barkalow@iabervon.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

transport.c

@@ -912,32 +912,31 @@ static int external_specification_len(const char *url)
 
 struct transport *transport_get(struct remote *remote, const char *url)
 {
+	const char *helper;
 	struct transport *ret = xcalloc(1, sizeof(*ret));
 
 	if (!remote)
 		die("No remote provided to transport_get()");
 
 	ret->remote = remote;
+	helper = remote->foreign_vcs;
 
 	if (!url && remote && remote->url)
 		url = remote->url[0];
 	ret->url = url;
 
-	/* In case previous URL had helper forced, reset it. */
-	remote->foreign_vcs = NULL;
-
 	/* maybe it is a foreign URL? */
 	if (url) {
 		const char *p = url;
 
 		while (isalnum(*p))
 			p++;
 		if (!prefixcmp(p, "::"))
-			remote->foreign_vcs = xstrndup(url, p - url);
+			helper = xstrndup(url, p - url);
 	}
 
-	if (remote && remote->foreign_vcs) {
-		transport_helper_init(ret, remote->foreign_vcs);
+	if (helper) {
+		transport_helper_init(ret, helper);
 	} else if (!prefixcmp(url, "rsync:")) {
 		ret->get_refs_list = get_refs_via_rsync;
 		ret->fetch = fetch_objs_via_rsync;