INT 15 - DESQview/X 1.02+ - DVDOS4GX.DVR - UNLOCK ??? MAILBOX                   
	AX = BFDEh
	BX = 0015h
	CX = index of ??? mailbox
		(0000h-0004h valid, but no range checking done)
Return: AX,BX destroyed
SeeAlso: AX=BFDEh/BX=0014h,AX=BFDEh/BX=0016h