Partially handle _NET_WM_BYPASS_COMPOSITOR

Unredirect the screen when some window sets _NET_WM_BYPASS_COMPOSITOR
to 1, but ignore the case where some window requests the screen to be
redirected by setting _NET_WM_BYPASS_COMPOSITOR to 2.

Closes #267

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/win.h

@@ -330,6 +330,10 @@ void win_update_leader(session_t *ps, struct managed_win *w);
  */
 // XXX was win_border_size
 void win_update_bounding_shape(session_t *ps, struct managed_win *w);
+/**
+ * Check if a window has BYPASS_COMPOSITOR property set
+ */
+bool win_is_bypassing_compositor(const session_t *ps, const struct managed_win *w);
 /**
  * Get a rectangular region in global coordinates a window (and possibly
  * its shadow) occupies.