addrequest/discardrequest send duplicate emails

[milki]

Both servlets AddRequest and DiscardRequest send duplicate emails to the request user. These two are different from the other *Request servlets because they can accept multiple request ids.

The final select query:

    request_query = db.push_requests.select().where(
        db.push_requests.c.id.in_(self.request_ids))

somehow duplicates the 1st request in the list. I first discovered this while working on #20 but discovered it in master as well.