Cause planner to account for evaluation costs in targetlists and

Cause planner to account for evaluation costs in targetlists and
HAVING quals.  Normally this is an insignificant effect --- but it
will not be insignificant when these clauses contain sub-selects.
The added costs cannot affect the planning of the query containing
them, but they might have an impact when the query is a sub-query
of a larger one.