Changed state attribs to direct access.

Changed the window states (focused, iconified and visible) to query the
system directly.

THIS IS A BREAKING CHANGE, although a fairly obscure one.  It affects
applications that both care about telling actual key events from
synthetic ones, and are implemented in a non-self-synchronizing way, and
that poll the GLFW_FOCUSED window attribute instead of using the window
focus callback.

If you maintain one of these, please feel free to drop me an email and
I'll help any way I can to transition your application to 3.1.

Fixes #189.
Fixes #204.

src/wl_window.c

@@ -307,6 +307,24 @@ void _glfwPlatformHideWindow(_GLFWwindow* window)
     wl_surface_commit(window->wl.surface);
 }
 
+int _glfwPlatformWindowFocused(_GLFWwindow* window)
+{
+    // TODO
+    return GL_FALSE;
+}
+
+int _glfwPlatformWindowIconified(_GLFWwindow* window)
+{
+    // TODO
+    return GL_FALSE;
+}
+
+int _glfwPlatformWindowVisible(_GLFWwindow* window)
+{
+    // TODO
+    return GL_FALSE;
+}
+
 void _glfwPlatformPollEvents(void)
 {
     struct wl_display* display = _glfw.wl.display;