INT 13,6 - Format Track and Set Bad Sector Flags (XT & portable)

	AH = 06
	AL = Interleave value (XT only)
	BX = format buffer, size = 512 bytes;  the first
	     2*(sectors/track) bytes contain F,N for each sector
	     F = 00h for good sector,
	     F = 80h for bad sector
	     N = sector number


	on return:
	AH = status  (see INT 13,STATUS)
	CF = 0 if successful
	   = 1 if error


	- BIOS disk write attempts should reset the controller on error
	- only the disk number is checked for validity