There is a need to be able to query all items in a collection.
And also in a Sequence, though we could cheat by converting all sequnecs to 
collections on input.

See eg the items in http://www.ithaka.org/about-ithaka/events/calendar-of-
events/previous-events/RSS
which are a sequence.  Selecting one items and doing 'find all' shoul d bring 
all of them in, not just the one wiht say rdf:_3