Implement Debug for PollEvented<E> if E implements Debug

Useful, esp since mio::unix::EventedFd already implements Debug.

Signed-off-by: Andy Grover <[email protected]>

src/reactor/poll_evented.rs

@@ -6,6 +6,7 @@
 //! acquisition of a token, and tracking of the readiness state on the
 //! underlying I/O primitive.
 
+use std::fmt;
 use std::io::{self, Read, Write};
 use std::sync::atomic::{AtomicUsize, Ordering};
 
@@ -43,6 +44,12 @@ pub struct PollEvented<E> {
     io: E,
 }
 
+impl<E: mio::Evented + fmt::Debug> fmt::Debug for PollEvented<E> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{{PollEvented {:?}}}", self.io)
+    }
+}
+
 impl<E: mio::Evented> PollEvented<E> {
     /// Creates a new readiness stream associated with the provided
     /// `loop_handle` and for the given `source`.