Decimal parameter conversion and normalization
    
    Parameter Decimal does not have a sufficient value checks. Some values
    cause Decimal parameter with a custom precision to crash with
    an unhandled exception.
    
    Improve parameter conversion and normalization operations to handle
    decimal exceptions more gracefully. Decimal parameter now also has
    new attributes enabling 2 new validation/normalization methods:
     * exponential: when False, decimal number is normalized to its
                    non-exponential form
     * numberclass: a set of allowed decimal number classes
                    (e.g. +Infinity, -Normal, ...) that are enforced
                    for every Decimal parameter value
    
    https://fedorahosted.org/freeipa/ticket/2705