Fix an obsolete comment on the whereRangeScanEst() routine.  No
changes to code.
Make sure the estLog() routine in the query planner handles negative
values correctly (always returning 1).  Prior to this change, estLog(-1)
would return a large number which could throw off the cost computations
in the query planner in obscure circumstances.
Add a test case to ensure that estLog() works for negative numbers.