INT 21 U - CUBIT v4.00 - GET CUBIT INT 21 HANDLER                               
	AX = 69FFh
	DX = 0000h
	BX = CB00h (magic value)
Return: ES:BX -> CUBITR.EXE handler for INT 21
InstallCheck:	test that the first eight bytes at the returned interrupt
	  handler are EBh 07h "CUBITR" (a short jump around the signature
	  followed by the signature)
Note:	the byte following the signature (i.e. ES:[BX+8]) indicates whether
	  CUBITR is active (01h) or disabled (00h)
SeeAlso: AX=69FFh/DX=CFBFh
Index:	installation check;CUBIT