ScalarArrayOpExpr when possible, that is, whenever there is an array type
for the values of the expression list.  This completes the project I've
been working on to improve the speed of index searches with long IN lists,
as per discussion back in mid-October.

I did not force initdb, but until you do one you will see failures in the
"rules" regression test, because some of the standard system views use IN
and their compiled formats have changed.