INT E0 - REAL/32 - "P_EXITCODE" - GET/SET PROCESS EXIT CODE
	CL = 5Eh
	DX = exit code or FFFFh to get
	    DH ignored when setting code
	    DL = process exit code
Return: AX = status (FFFFh on error)
	if getting:
	    AH = termination reason
		00h normal
		01h external termination via Ctrl-C or P_ABORT
		02h hardware (critical) error abort
		03h child did not terminate
		FFh illegal request (no child, or exit code already retrieved)
	    AL = process exit code
SeeAlso: INT E0/CL=5Dh,INT 21/AH=4Ch