INT 21 - LANtastic - COPY FILE                                                  
	AX = 5F97h
	CX:DX = number of bytes to copy (FFFFFFFFh = entire file)
	SI = source file handle
	DI = destination file handle
Return: CF clear if successful
	    DX:AX = number of bytes copied
	CF set on error
	    AX = error code
Note:	copy is performed by server