Function RDEF(efn:Event_flag):Boolean;
   EXTERNAL;
{*USER*
 Pascal-3 Function which returns status of given event flag.
All efns are serviced - including group globals.
 $DSW holds status of internal RDXF call on exit: this will
be IS.CLR (0) if group globals do not exist. However, the
return status will be correct (assuming the requested flag
is not group global).
}