Implement TryFrom to transform various I/O primitives into their mio counterparts (#1158)

* `TryFrom<TcpListener> for mio::net::TcpListener`
* `TryFrom<TcpStream> for mio::net::TcpStream`
* `TryFrom<UdpSocket> for mio::net::UdpSocket`
* `TryFrom<UnixListener> for mio_uds::UnixListener`
* `TryFrom<UnixStream> for mio_uds::UnixStream`

tokio-udp/src/socket.rs

@@ -1,6 +1,7 @@
 use super::{RecvDgram, SendDgram};
 use futures::{try_ready, Async, Poll};
 use mio;
+use std::convert::TryFrom;
 use std::fmt;
 use std::io;
 use std::net::{self, Ipv4Addr, Ipv6Addr, SocketAddr};
@@ -418,6 +419,18 @@ impl UdpSocket {
     }
 }
 
+impl TryFrom<UdpSocket> for mio::net::UdpSocket {
+    type Error = io::Error;
+
+    /// Consumes value, returning the mio I/O object.
+    ///
+    /// See [`tokio_reactor::PollEvented::into_inner`] for more details about
+    /// resource deregistration that happens during the call.
+    fn try_from(value: UdpSocket) -> Result<Self, Self::Error> {
+        value.io.into_inner()
+    }
+}
+
 impl fmt::Debug for UdpSocket {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         self.io.get_ref().fmt(f)