Added a factory class for creating JXPathContext objects.

This class simplifies testing of the XPath expression engine.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/branches/immutableNodes@1565799 13f79535-47bb-0310-9956-ffa450edef68
ConfigurationNodePointerFactory now supports arbitrary nodes with a handler.

A specialized node wrapper instance is created to detect configuration nodes
and to associate them with the correct node handler.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/branches/immutableNodes@1565800 13f79535-47bb-0310-9956-ffa450edef68