AddEnum

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** add a new enum type
        arguments:      idx - serial number of the new enum.
                              If another enum with the same serial number
                              exists, then all enums with serial
                              numbers >= the specified idx get their
                              serial numbers incremented (in other words,
                              the new enum is put in the middle of the list
                              of enums).
                              If idx >= GetEnumQty() then the new enum is
                              created at the end of the list of enums.
                        name - name of the enum.
                        flag - flags for representation of numeric constants
                               in the definition of enum.
        returns:        id of new enum or -1.

long AddEnum(long idx,string name,long flag);