Compatibility: Win 3.x
Expects: AX    1600H
                                                                  
Returns: AX    if Enhanced-Mode Windows is not running, AL=00H or AL=80H.
if Enh386 Win 3.x+ is installed: AL = major version number
AH = minor version number
if Win/386 2.x is installed AL=01H or ffH
                                                                  
Info: You may use this service to see if you are running is a DOS
session under Enhanced-Mode Windows.

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INT 2fH 1600H: Is Enh386 Windows Installed?