Add test for LookupHost iterator Send/Sync traits

src/test/run-pass/sync-send-in-std.rs

+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(lookup_host)]
+
+use std::net::lookup_host;
+
+fn is_sync<T>(_: T) where T: Sync {}
+fn is_send<T>(_: T) where T: Send {}
+
+macro_rules! all_sync_send {
+    ($ctor:expr, $($iter:ident),+) => ({
+        $(
+            let mut x = $ctor;
+            is_sync(x.$iter());
+            let mut y = $ctor;
+            is_send(y.$iter());
+        )+
+    })
+}
+
+fn main() {
+    all_sync_send!(lookup_host("localhost").unwrap(), next);
+}