LUCENE-5254: don't hold ref to original SR from SCR, to avoid bounded leak of things like live docs bitset

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1529135 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5254: just pass 'this' to the CoreClosedListeners

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1529139 13f79535-47bb-0310-9956-ffa450edef68