INT 2F U - DRIVER.SYS support - INSTALLATION CHECK
AX = 0800h
Return: AL = status
00h not installed, OK to install
01h not installed, not OK to install
FFh installed
Desc: determine whether the internal support code used by DRIVER.SYS is
present; it is always present in DOS 3.2+
Note: supported by DR DOS 5.0 and Novell DOS 7