Do not attempt to create an automatic index on a constant constraint, as
doing so is pointless.
Allow an automatic index on a WHERE constraint where the RHS is does not
reference another table as long as the RHS is not a constant.
Simplification to the logic that prevents automatic indexes from being formed
on constant expressions.
A different approach to the autoindex problem that deletes query-planner code
rather than adding it.
Add the autoindex2.test testing module.
Improvements to query planning, especially in regards to estimating the
cost and benefit of automatic indexes.
Add the likely() function for symmetry with unlikely().  The likely(X)
function means the same thing as likelihood(X,0.9375).
Fix a missing space in a "wheretrace" comment.  No changes to production code.