INT 2F,8 - DRIVER.SYS Support (Undocumented DOS 3.2+)

	AH = 08
	AL = 00  installation check
	   = 01  add new block device
	   = 02  execute device driver request
	   = 03  get drive data table list (DOS 4.0+)
	DS:DI = pointer to drive data table  (AL=01)
	ES:BX = pointer to device driver request header (AL=02)


	on return:
	AL = 00  not installed, ok to install (AL=00)
	   = 01  not installed, do NOT install (AL=00)
	   = FF  installed (AL=00)
	ES:BX = updated device request header (AL=02)

	- function 01 scans DOS's drive data tables and appends the new
	  data table to to the chain.  All tables referencing the same
	  physical drive are updated