Udp socket readiness methods (#522)

tokio-tcp/src/stream.rs

@@ -159,10 +159,7 @@ impl TcpStream {
     ///
     /// # Panics
     ///
-    /// This function panics if:
-    ///
-    /// * `ready` contains bits besides `writable` and `hup`.
-    /// * called from outside of a task context.
+    /// This function panics if called from outside of a task context.
     pub fn poll_write_ready(&self) -> Poll<mio::Ready, io::Error> {
         self.io.poll_write_ready()
     }