Revert "remove url from --set"

This reverts commit f44a586.

Since "url" is no longer in the variables array, it is not necessary to
explictly reject it.

trurl.c

@@ -351,8 +351,6 @@ static void setadd(struct option *o,
                    const char *set) /* [component]=[data] */
 {
   struct curl_slist *n;
-  if(!strncmp("url", set, 3))
-    errorf(ERROR_SET, "--set does not support url, use --redirect instead");
   n = curl_slist_append(o->set_list, set);
   if(n)
     o->set_list = n;
@@ -362,8 +360,6 @@ static void iteradd(struct option *o,
                     const char *iter) /* [component]=[data] */
 {
   struct curl_slist *n;
-  if(!strncmp("url", iter, 3))
-    errorf(ERROR_ITER, "--iterate does not support url");
   n = curl_slist_append(o->iter_list, iter);
   if(n)
     o->iter_list = n;