Add Expose event handler which is needed on some window managers.

src/events.rs

@@ -34,6 +34,9 @@ pub enum Event {
 
     /// The event loop was woken up by another thread.
     Awakened,
+
+    /// The window needs to be redrawn.
+    Refresh,
 }
 
 pub type ScanCode = u8;

src/x11/window/mod.rs

@@ -161,6 +161,11 @@ impl<'a> Iterator for PollEventsIterator<'a> {
                     }
                 },
 
+                ffi::Expose => {
+                    use events::Event::Refresh;
+                    return Some(Refresh);
+                },
+
                 ffi::MotionNotify => {
                     use events::Event::MouseMoved;
                     let event: &ffi::XMotionEvent = unsafe { mem::transmute(&xev) };