NUTCH-356 Plugin repository cache can lead to memory leak

git-svn-id: https://svn.apache.org/repos/asf/nutch/trunk@1560985 13f79535-47bb-0310-9956-ffa450edef68
NUTCH-1715 RobotRulesParser adds additional * to the robots name

git-svn-id: https://svn.apache.org/repos/asf/nutch/trunk@1561087 13f79535-47bb-0310-9956-ffa450edef68
NUTCH-1717 HostDB not to complain if filters/normalizers are disabled

git-svn-id: https://svn.apache.org/repos/asf/nutch/trunk@1562058 13f79535-47bb-0310-9956-ffa450edef68