valFn = function (v) {
            if (v == null) return true;
            return (v === true) || (v === false);
        }
Returns a standard boolean data type Validator.
    @example
        // Assume em1 is a preexisting EntityManager.
        var productType = em1.metadataStore.getEntityType("Product");
        var discontinuedProperty - productType.getProperty("Discontinued");
        // Validates that the value of the Discontinued property on Product is a boolean
        discontinuedProperty.validators.push(Validator.bool());
    @method bool
    @static
    @return {Validator} A new Validator