make secondary ordering of facet.field values (and facet.pivot?) consistently deterministic

as a fluke of how the SOLR-2894 patch evolved, it wound up adding a bit of testing of distributed facet.field on date fields (see r1617789 changes to TestDistributedSearch) ... but this started triggering some random failures due to facet constraints with identical values being sorted differently between the distributed query and the single node control query.

We should make the facet.field (and facet.pivot) code order constraints with tied counts consistently regardless of whether it's a distrib search or not.