SOLR-4765: The new Collections API test deleteCollectionWithDownNodes fails often with a server 500 error.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1475869 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-4738: only CheckIndex when the last commit is > segments_1

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1475905 13f79535-47bb-0310-9956-ffa450edef68
fix test bug

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1475920 13f79535-47bb-0310-9956-ffa450edef68
SOLR-4761: add option to plug in mergedSegmentWarmer

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1476026 13f79535-47bb-0310-9956-ffa450edef68