Enhance the logest.c utility with new operators: "dup", "inv", "log", and
"nlogn".  Provide help on an invalid input.
Minor cleanup of the code in the query planner that computes the costs 
estimates for the various plans.  There are no changes to the costs at this
time.  But the code is slightly more readable now and that might facilitate
future enhancements.
Enhance the sqlite3VdbeRecordCompare() routines so that if they encounter
database corruption, they will set the UnpackedRecord.isCorrupt field and
return 0.  The sqlite3BtreeMovetoUnpacked() routine detects this and returns
SQLITE_CORRUPT, causing the corruption to be reported back to the top-level.