XPdosValue()
   returns the current DOS version as a number
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   Function:   XPdosValue()

               returns the current DOS version as real number, could be
               used instead of XPdosMinor() and XPdosMajor(). XPdosValue()
               is in fact XPdosMajor() + (XPdosMinor()/100).

   Syntax:     XPdosValue() --> nVersion

   Arguments:  None

   Returns:    A number representing the DOS version.

   Usage:      if XPdosValue() < 3.30
                        ? 'Need DOS 3.30+ to Run, Sorry.'
                        QUIT
               End