Introduce a WindowProxy for accessing a subset of functionality

from other threads. This currently provides a way for other threads
to wakeup a blocked event loop on X11. Other platforms have stub
functions that need to be implemented. This is similar to
the functionality of glfwPostEmptyEvent.

src/osx/mod.rs

@@ -74,6 +74,16 @@ impl Window {
     }
 }
 
+#[cfg(feature = "window")]
+#[deriving(Clone)]
+pub struct WindowProxy;
+
+impl WindowProxy {
+    pub fn wakeup_event_loop(&self) {
+        // TODO
+    }
+}
+
 extern fn window_should_close(this: id, _: id) -> id {
     unsafe {
         let mut stored_value = ptr::null_mut();
@@ -278,6 +288,10 @@ impl Window {
         unimplemented!()
     }
 
+    pub fn create_window_proxy(&self) -> WindowProxy {
+        WindowProxy
+    }
+
     pub fn poll_events(&self) -> Vec<Event> {
         let mut events = Vec::new();