Allow the configuration to specify the ordering of the groupings
Do not assume that PostLoadCheck normalized to arrayrefs

The irevious commit normalized hashrefs into sorted arrayrefs during the
PostLoadCheck.  However, this is insufficient to cope with configuration
settings which are altered at run-time, after PostLoadChecks have been
run -- which include tests.  Adjust ->Groupings and ->LimitToGrouping to
cope with hashrefs as well.
Merge branch '4.2/grouping-ordering'