Refactor the ORDER BY optimizer in the NGQP so that it is easier to maintain
and so that it can support optimizing out GROUP BY and DISTINCT clauses.
Fix a display issue with EXPLAIN QUERY PLAN.
Increase the estimated full-scan cost for an FTS3 table.
Better determination of when an index is UNIQUE.
Test case updates.
Get the index-only optimization working for OR queries.
Restore the PRAGMA reverse_unordered_selects behavior.
Update some variable names and comments in the ORDER BY optimizer.  Fix a
bug in the ORDER BY optimizer dealing with IS NULL constraints.  Updates
to test cases.