Expose the 'more_results' value fetched from the back-end.

Include notes that it is known to be currently un-useful, since the
back-end sets it to indicate there are more results willy-nilly.

Fixes #423.
Merge pull request #425 from tseaver/423-expose_query_more_results

Fix #423:  Expose the 'more_results' value fetched from the back-end.
Changing Query.filter to ask for operator and prop. name separately.

Also adding a test for property names with spaces in them.

Fixes #424.