INT 2F U - DOS 3.0+ internal - SET DRIVE???                                     
	AX = 1219h
	SS = DOS DS (must be using a DOS internal stack)
	STACK: WORD drive (0 = default, 1 = A:, etc)
Return: ???
	STACK unchanged
Notes:	calls AX=1217h
	builds a current directory structure if inside server call
	  (INT 21/AX=5D00h)
SeeAlso: AX=1217h,AX=121Fh