Remove a redundant test case (probably a copy/paste error).  Add an assert()
to where.c to ensure that automatic indexes do not have there output row 
counts adjusted downward by supplementary constraints.
Deploy heuristics (well-commented) to better estimate how much unindexed terms
in the WHERE clause filter the number of output rows from a single table.
Fix an error in the comments from the previous check-in.
Always reinitialized the Index.bUnordered and Index.noSkipscan flags before
rereading the sqlite_stat1 table, even if SQLITE_ENABLE_STAT4 is defined.