INT 21 - DOS 4.x only - internal - GET DOS SWAPPABLE DATA AREAS

	AX = 5D0Bh
Return: CF set on error
	    AX = error code (see #01680)
	CF clear if successful
	    DS:SI -> swappable data area list (see #01689)
Notes:	copying and restoring the swappable data areas allows DOS to be
	  reentered unless it is in a critical section delimited by calls to
	  INT 2A/AH=80h and INT 2A/AH=81h,82h
	SHARE and other DOS utilities consult the byte at offset 04h in the
	  DOS data segment (see INT 2F/AX=1203h) to determine the SDA format
	  in use: 00h = DOS 3.x, 01h = DOS 4.0-6.0, other = error.
	DOS 5+ use the SDA format listed below, but revert back to the DOS 3.x
	  call for finding the SDA (see #01687); Novell DOS 7 does not support
	  this function, either.
SeeAlso: AX=5D06h,INT 2A/AH=80h,INT 2A/AH=81h,INT 2A/AH=82h,INT 2F/AX=1203h