procedure waitw(efn:event_flag;
                   Count: Integer;
                   Units: Time_Unit
  		);
   EXTERNAL;
{*USER*
 Procedure waitw issues a MRKT directive, followed by a WAIT for efn.
The result is to halt the calling task for the specified duration.
The WAIT is not issued if the MRKT directive fails. Works with
all event flags.
 Directive status is available in $DSW on return.
 Companion procedure WAIT issues a STOP for efn, rather than a
WAIT for efn - which is generally better. If you don't know the
difference, or don't care, use WAIT rather then WAITW.
}