Change the recursive common table expression algorithm to use a queue instead
of a pair of tables.  Runs about 25% faster on the sudoku solver query. 
The OP_SwapCursors opcode is no longer required.  The current implementation
uses just a fifo, but the plan is to change it into a queue that will support 
ORDER BY and LIMIT in a recursive query.
Remove an unnecessary parameter from selectInnerLoop().  Clean up comments.
Fix a typo in a comment. No changes to code or tests.
Add new SelectDest codes, SRT_Queue and SRT_DistQueue in anticipation of adding
ORDER BY support on recursive queries.  Factor out the recursive query
code generator into a separate procedure.
Get ORDER BY working for recursive queries.
Update the spellfix virtual table to optimize queries of the form "SELECT ... FROM tbl WHERE rowid=?".
Add support for LIMIT and OFFSET in a recursive query.
Change the WITH RECURSIVE implementation to use a queue instead of a pair of
tables.  Add support for ORDER BY, LIMIT, and OFFSET on recursive queries.
Fix harmless compiler warnings.
Avoid an extra seek when inserting records into the epheremal index used to ensure that rows returned by UNION recursive queries are unique.