InstallUserDriver function

  DECLARATION:  InstallUserDriver(Name : String;
                         AutoDetectPtr : Pointer)

      PURPOSE:  Adds a vendor-added device to the BGI driver table

         UNIT:  Graph

  RESULT TYPE:  Word

      REMARKS:  The parameter, Name is the filename of the vendor
                supplied device driver to be added.  AutoDetectPtr is a
                pointer to an optional autodetect function that accompanies
                some drivers.  The autodetect function requires no parameters
                and returns an Integer.