Fix a formatting error ("%d" needed in place of "%g") on a WHERETRACE
macro inside of the query planner.  This fix applies to debugging logic
only.
Fix a problem causing an inaccurate stat4-based estimate for the number of rows visited by a range scan.
Add a testcase() macro to help verfity the row estimation logic.
Fix a problem causing an inaccurate stat4-based estimate for the
number of rows visited by a range scan.
Improved WHERETRACE messages for the estimated output row reductions from
range scans.