FTP: make the data connection work when going through proxy

This is a regression since the switch to always-multi internally
c43127414d.

Test 1316 was modified since we now clearly call the Curl_client_write()
function when doing the LIST transfer part and then the
handler->protocol says FTP and ftpc.transfertype is 'A' which implies
text converting even though that the response is initially a HTTP
CONNECT response in this case.

lib/connect.c

@@ -777,7 +777,7 @@ CURLcode Curl_is_connected(struct connectdata *conn,
       /* we are connected with TCP, awesome! */
 
       /* see if we need to do any proxy magic first once we connected */
-      code = Curl_connected_proxy(conn);
+      code = Curl_connected_proxy(conn, sockindex);
       if(code)
         return code;