Bugfix: Fix screen wrapping, cleanup some log messages

Before this fix, you could go upwards and select the screen which
was at the rightmost because it also was the one topmost (if all
screen’s top position is equal).

include/client.h

@@ -97,4 +97,10 @@ void client_unmap(xcb_connection_t *conn, Client *client);
  */
 void client_map(xcb_connection_t *conn, Client *client);
 
+/**
+ * Pretty-prints the client’s information into the logfile.
+ *
+ */
+void client_log(Client *client);
+
 #endif