Pull up waitingRequests.
NIO2 used a ConcurrentHashMap whereas BIO and APR/native used a Queue. Switch to ConcurrentHashMap for all since what we really want here is a Set (and there isn't a ConcurrentHashSet implementation).

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1601583 13f79535-47bb-0310-9956-ffa450edef68