Observed strange lock-up on OSX when two threads were writing concurrently to this Map. Switch to ConcurrentHashMap in an attempt to avoid the lock-up in future.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1551428 13f79535-47bb-0310-9956-ffa450edef68
Need to publish new tomcat-util-scan JAR

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1551431 13f79535-47bb-0310-9956-ffa450edef68