Only send WM_TAKE_FOCUS when the client supports it in the protocols atom

Fixes opening xterm, for example

include/xcb.h

@@ -116,6 +116,12 @@ void fake_configure_notify(xcb_connection_t *conn, Rect r, xcb_window_t window);
  */
 void fake_absolute_configure_notify(Con *con);
 
+/**
+ * Sends the WM_TAKE_FOCUS ClientMessage to the given window
+ *
+ */
+void send_take_focus(xcb_window_t window);
+
 /**
  * Finds out which modifier mask is the one for numlock, as the user may
  * change this.