LUCENE-5222: fix expression sort with executorService

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1524575 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5220: ExpressionSortField has crappy toString/bad equals/hashcode

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1524588 13f79535-47bb-0310-9956-ffa450edef68