Added NodeHandlerDecorator class.

This base class provides basic functionality for adapting a NodeHandler to
special requirements.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/branches/immutableNodes@1580602 13f79535-47bb-0310-9956-ffa450edef68
Fixed a problem with list delimiter handling in hierarchical configurations.

AbstractHierarchicalConfiguration must override addPropertyInternal() rather
than addPropertyDirect() to guarantee correct list delimiter handling.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/branches/immutableNodes@1580603 13f79535-47bb-0310-9956-ffa450edef68