remove dead states after union(), just like intersection() and complement() do

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1607139 13f79535-47bb-0310-9956-ffa450edef68
SOLR-2245: Numerous improvements to the MailEntityProcessor

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1607147 13f79535-47bb-0310-9956-ffa450edef68