Implement CAST(<string> AS <datetime>) and <datetime> + <interval>.
Add EquiJoinRel, base class for joins known to be equi-joins.
Tune ImmutableIntList's iterators.
Remove the 2-minute wait at the top of the hour for tests of CURRENT_TIME, etc.

For a little variety, we still do it the old way if -Doptiq.test.slow=true.