func (agg aggregate) Errors() []error {
	return []error(agg)
}

// Matcher is used to match errors.  Returns true if the error matches.
type Matcher func(error) bool

// FilterOut removes all errors that match any of the matchers from the input
// error.  If the input is a singular error, only that error is tested.  If the
// input implements the Aggregate interface, the list of errors will be