[NEXUS-5822] replace the call to ConcurrentHashMap.containsKey with the content of that method in Java 8 b102 with get prefixed by super. thereby preventing the recursion
work arround a compile time issue with Java 8's ConcurrentHashMap for HierarchichalMap by delegating to an internal ConcurrentHashMap rather than extending it
removed the commented extension of ConcurrentHashMap
Merge pull request #89 from lhochet/nexus-oss-2.6.0.x-NEXUS-5822

WIP: Java8 incompatibility with appcontext impl using containsKey()