INT 21 - DOS 4.0+ - EXTENDED OPEN/CREATE                                        
	AX = 6C00h
	BL = open mode as in AL for normal open (see also AH=3Dh)
	    bit 7: inheritance
	    bits 4-6: sharing mode
	    bit 3 reserved
	    bits 0-2: access mode
		100 read-only, do not modify file's last-access time (DOS 7.0)
	BH = flags
	    bit 6 = auto commit on every write (see also AH=68h)
	    bit 5 = return error rather than doing INT 24h
	    bit 4 = (FAT32) extended size (allow 4GB files instead of 2GB)
	CX = create attribute (see #01769)
	DL = action if file exists/does not exist (see #01770)
	DH = 00h (reserved)
	DS:SI -> ASCIZA NUL-terminated ASCII string.	The ASCIZ string "ABC" consists of the four bytes 41h, 42h, 43h, and 00h.  Unless otherwise specified, maximum lengths given in the interrupt list do not include the terminating NUL. file name
Return: CF set on error
	   AX = error code (see #01680 at AH=59h/BX=0000h)
	CF clear if successful
	   AX = file handle
	   CX = status (see #01768)
Notes:	the PCIBM PC LAN Program only supports existence actions (in DL) of 01h,
	  10h with sharing=compatibility, and 12h
	DR DOS reportedly does not support this function and does not return
	  an "invalid function call" error when this function is used.
	the documented bits of BX are stored in the SFTsee System File Table when the file is opened
	  (see #01641,#01642)
BUG:	this function has bugs (at least in DOS 5.0 and 6.2) when used with
	  drives handled via the network redirector (INT 2F/AX=112Eh):
	    - CX (attribute) is not passed to the redirector if DL=11h,
	    - CX does not return the status, it is returned unchanged because
	      DOS does a PUSH CX/POP CX when calling the redirector.
SeeAlso: AH=3Ch,AH=3Dh,AX=6C01h,AX=7160h/CL=00h,INT 2F/AX=112Eh

(Table 01768)
Values for extended open function status:
 01h	file opened
 02h	file created
 03h	file replaced

Bitfields for file create attribute:
Bit(s)	Description	(Table 01769)
 6-15	reserved
 5	archive
 4	reserved
 3	volume label
 2	system
 1	hidden
 0	readonly

Bitfields for action:
Bit(s)	Description	(Table 01770)
 7-4	action if file does not exist
	0000 fail
	0001 create
 3-0	action if file exists
	0000 fail
	0001 open
	0010 replace/open