Work around curl-gnutls not liking to be reinitialized

curl versions 7.16.3 to 7.18.0 included had a regression in which https
requests following curl_global_cleanup/init sequence would fail with ASN1
parser errors with curl-gnutls. Such sequences happen in some cases such
as git fetch.

We work around this by removing the http_init and http_cleanup calls from
get_refs_via_curl, replacing them with a transport->data initialization
with the http_walker (which does http_init).

While the http_walker is not currently used in get_refs_via_curl, http
and walker code refactor will make it use it.

Signed-off-by: Mike Hommey <mh@glandium.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

transport.c

@@ -441,11 +441,12 @@ static struct ref *get_refs_via_curl(struct transport *transport)
 	struct ref *ref = NULL;
 	struct ref *last_ref = NULL;
 
+	if (!transport->data)
+		transport->data = get_http_walker(transport->url);
+
 	refs_url = xmalloc(strlen(transport->url) + 11);
 	sprintf(refs_url, "%s/info/refs", transport->url);
 
-	http_init();
-
 	slot = get_active_slot();
 	slot->results = &results;
 	curl_easy_setopt(slot->curl, CURLOPT_FILE, &buffer);
@@ -473,8 +474,6 @@ static struct ref *get_refs_via_curl(struct transport *transport)
 		return NULL;
 	}
 
-	http_cleanup();
-
 	data = buffer.buf;
 	start = NULL;
 	mid = data;