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/system/proctl.c

@@ -47,8 +47,8 @@ register message *m_ptr;	/* pointer to request message */
   rpc->p_ldt_sel = old_ldt_sel;
 #endif
   rpc->p_nr = m_ptr->PR_PROC_NR;	/* this was obliterated by copy */
-
-  rpc->p_flags |= NO_MAP;	/* inhibit the process from running */
+  rpc->p_ntf_q = NULL;			/* remove pending notifications */
+  rpc->p_flags |= NO_MAP;		/* inhibit process from running */
 
   rpc->p_flags &= ~(PENDING | SIG_PENDING | P_STOP);