fails:Enumerator#rewind resets the enumerator to its initial state
fails:Enumerator#rewind returns self
fails:Enumerator#rewind has no effect on a new enumerator
fails:Enumerator#rewind has no effect if called multiple, consecutive times
fails:Enumerator#rewind works with peek to reset the position
fails:Enumerator#rewind calls the enclosed object's rewind method if one exists
fails:Enumerator#rewind does nothing if the object doesn't have a #rewind method
fails:Enumerator#rewind clears a pending #feed value
