Events loop backend (#269)

* Don't use UNIX_BACKEND in Window2::new

* Move get_available_monitors and get_primary_monitor to EventsLoop

* Remove UNIX_BACKEND

* Restore choosing the Linux backend

* Return a XNotSupported for new_x11()

* Fix fullscreen example

src/platform/linux/x11/mod.rs

@@ -120,6 +120,12 @@ impl EventsLoop {
         result
     }
 
+    /// Returns the `XConnection` of this events loop.
+    #[inline]
+    pub fn x_connection(&self) -> &Arc<XConnection> {
+        &self.display
+    }
+
     pub fn create_proxy(&self) -> EventsLoopProxy {
         EventsLoopProxy {
             pending_wakeup: Arc::downgrade(&self.pending_wakeup),
@@ -675,12 +681,11 @@ lazy_static! {      // TODO: use a static mutex when that's possible, and put me
 }
 
 impl Window2 {
-    pub fn new(events_loop: &::platform::EventsLoop,
+    pub fn new(x_events_loop: &EventsLoop,
                window: &::WindowAttributes,
                pl_attribs: &PlatformSpecificWindowBuilderAttributes)
                -> Result<Self, CreationError>
     {
-        let x_events_loop = if let ::platform::EventsLoop::X(ref e) = *events_loop { e } else { unreachable!() };
         let win = ::std::sync::Arc::new(try!(Window::new(&x_events_loop, window, pl_attribs)));
 
         // creating IM