should fix issue 303

The idea is to let the underlying ResultSet handle since_id/max_id as used to generate subsequent API requests.

The since_id/max_id returned in the twitter search results metadata do not generally reflect the actual min/max id's retrieved, as twitter copies them from the request when present. Imho it's best just to ignore them for now...

I haven't checked if the search API returns most recent tweets first, but I think that's most probably the case.