bugfix (#ifdef DEBUG) for short lived windows

add_window()  should contain:

         w->plist = Qnil;
         w->frame_style = Qnil;
         w->frame = 0;
         
+         w->name = rep_null_string ();
         w->icon_image = rep_NULL;

because the 1st X call (which is _before_ XGetWMName), can cause the 
error_handler
call:
        DB(("error_handler (%s)\n", rep_STR(w->name)));

and 0 is not valid for rep_STR.




Also, i'm not sure if an infinite cycle is avoided (when closing windows):

remove_window() makes some X calls, which (if the X window is already gone),
can trigger error_handler, which calls remove_window. 


i've added a new slot    u_int status : 2;  to lisp_window   to avoid it.