LUCENE-2878: Make Interval package-private, remove PositionsCollector

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene2878@1643787 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-2878: Remove positions highlighter (for now); MemoryPostingsFormat fix

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene2878@1643788 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-2878: Remove postingsFeatures() from Collector

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene2878@1643791 13f79535-47bb-0310-9956-ffa450edef68