LUCENE-6096: Improve and test LRUFilterCache.ramBytesUsed.


git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1644582 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-6095: Remove RamUsageTester.IdentityHashSet and use Collections.newSetFromMap(new IdentityHashMap<E, Boolean>()) instead.


git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1644587 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-6096: Relax assertion about memory usage since memory usage depends on the JVM impl and settings.


git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1644594 13f79535-47bb-0310-9956-ffa450edef68