New NOTIFY trap (IPC call) to send queued notification messages.

The call works. Permission check, restriction of outstanding notifications
to be added. Low level code to make it work from within interrupt handlers
will be added as well.

kernel/type.h

@@ -40,7 +40,7 @@ struct notification {
   proc_nr_t 	 n_source;		/* sender of notification */
   notify_type_t	 n_type;		/* notification type */
   notify_arg_t 	 n_arg;			/* notification argument */
-  notify_flags_t n_fags;		/* notification flags */
+  notify_flags_t n_flags;		/* notification flags */
   struct notification* n_next;		/* pointer to next notification */
 };