SOLR-5577: Harden leaking Timer thread.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_4_6@1559589 13f79535-47bb-0310-9956-ffa450edef68
Backport this to 4.6, so we can be sure that next release has correct version and bootclasspath for "nice" javadocs:
Merged revision(s) 1547347 from lucene/dev/branches/branch_4x:
LUCENE-5355: Add support for -Dbootjdk to point to a separate JAVA_HOME that is used to generate javadocs; validate the -Dbootclasspath to point to a valid rt.jar

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_4_6@1559597 13f79535-47bb-0310-9956-ffa450edef68