INT 2F U - DOS 4.x DISPLAY.SYS internal - INSTALLATION CHECK???                 
	AX = AD10h
	???
Return: AX = FFFFh
	BX = ??? (0100h in PC-DOS 4.01)
                                                                                

INT 2F U - DOS 5+ DISPLAY.SYS internal - ???                                    
	AX = AD10h
	???
Return: CF clear if successful
	CF set on error
Note:	this function is a NOP if the active code page has never been set
	  (AX=AD02h returns BX=FFFFh); its purpose otherwise is not known