INT 15 - DESQview v2.20+ - SET ERROR HANDLING                                   
	AX = DE15h
	BL = error handling mode
	    00h post system error on all error conditions
	    01h return carry flag set on calls to ADDTO, SUBFROM, and WRITE
		messages sent to mailboxes which fail due to lack of system
		or common memory
	    02h (v2.26+) same as 01h, but also return null pointer for GETMEM
		calls which fail due to lack of system memory
Return: nothing
SeeAlso: AX=DE0Ch,AX=DE16h