)
Call NESL function RegisterEventConsumer with:
	BX = 0004h
	ES:SI -> Consumer Event Control Block (CECB) (see #03022)
Return: AX = completion code (0h, 8005h, 8008h) (see #03019)
	ES:SI -> still points to CECB
	BP,DS,STACK preserved
Desc:	Allows a module to register as a consumer of a given event class
Note:	on entry, the CECB_ClassName, CECB_NotifProc and CECB_OSILevel must be
	  filled in.
SeeAlso: #03014,#03018