LUCENE-4849: make ParallelTaxonomyArrays abstract

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1457810 13f79535-47bb-0310-9956-ffa450edef68
SOLR-4605: Rollback does not work correctly.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1457812 13f79535-47bb-0310-9956-ffa450edef68