quoted_date converts time objects to default_timezone

Looking for feedback on this ticket, which fixes some confusing
behavior with Time objects in find conditions:

https://rails.lighthouseapp.com/projects/8994/tickets/2946-quoted_date-converts-time-objects-to-default_timezone

Currently, if your database is in UTC, and you pass Time.now into find
conditions, ex:

    Article.all :conditions => ['posted_at < ?', Time.now]

you'll get a query for a time that will be off by your system's UTC
offset. This ticket fixes this.

The fix in this ticket will also allow AR time_zone_aware_attributes
to work with default_timezone == :local, a combination that doesn't
work correctly right now.