LUCENE-4952: add method to force DrillSideways to keep all sub-scorers on the doc being collected

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1471732 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-4952: put CHANGES entry in the right place

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1471733 13f79535-47bb-0310-9956-ffa450edef68