LUCENE-4930: Reduce contention in older/buggy JVMs when using AttributeSource#addAttribute() because java.lang.ref.ReferenceQueue#poll() is implemented using synchronization.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1467579 13f79535-47bb-0310-9956-ffa450edef68