The statistics after a sequence of inserts/deletes are updated asynchronously
in PBXT, causing unpredictable test results. Fix by running the test on a
fresh copy of the table with no deletes performed, to get stable results.
- Fix PBXT test results (PBXT doesn't support MRR or ICP, but we get result
diffs because we've also backported a fix that
- prints out "Using where" when the table has part of WHERE that it has
got from LEFT JOIN's ON expression
- Does a better job at removing equalities that are guaranteed to be true
by use of ref acccess.
