INT 21 - DOS 2+ internal - CREATE CHILD PSPsee Program Segment Prefix
	AH = 55h
	DX = segment at which to create new PSPsee Program Segment Prefix
	SI = (DOS 3.0+) value to place in memory size field at DX:[0002h]
Return: AL destroyed
Notes:	creates a "child" PSPsee Program Segment Prefix rather than making an exact copy of the current
	  PSPsee Program Segment Prefix; the new PSPsee Program Segment Prefix's parent pointer is set to the current PSPsee Program Segment Prefix and the
	  reference count for each inherited file is incremented
	(DOS 2.0+) sets current PSPsee Program Segment Prefix to DX
	(DOS 3.0+) marks "no inherit" file handles as closed in child PSPsee Program Segment Prefix
	this function is implemented using the same code as AH=26h, so unlike
	  other DOS 2+ functions, it does not return status in CF, instead
	  returning status in AL as DOS 1.x functions do (but it never puts an
	  explicit return value in AL)
SeeAlso: AH=26h,AH=50h