INT 2F - MDEBUG command driver - START DRIVER                                   
	AX = D111h
Return: DL = FFh
Notes:	only called by the transient part of the driver to inform the resident
	  part that it is installed
	the function must be reentrant and the driver mustn't chain this
	  function to the old INT 2F
SeeAlso: AX=D101h,AX=D112h