Bugfix: Track the user’s pointer over the root window and update current workspace (Thanks xeen)

When not having any windows on the first workspace, switching to the
second workspace using your mouse was not registered by i3.

include/handlers.h

@@ -35,6 +35,15 @@ int handle_key_press(void *ignored, xcb_connection_t *conn,
 int handle_enter_notify(void *ignored, xcb_connection_t *conn,
                         xcb_enter_notify_event_t *event);
 
+/**
+ * When the user moves the mouse but does not change the active window
+ * (e.g. when having no windows opened but moving mouse on the root screen
+ * and crossing virtual screen boundaries), this callback gets called.
+ *
+ */
+int handle_motion_notify(void *ignored, xcb_connection_t *conn,
+                         xcb_motion_notify_event_t *event);
+
 /**
  * Checks if the button press was on a stack window, handles focus setting and
  * returns true if so, or false otherwise.