Added new methods to NodeKeyResolver interface.

These methods are needed for doing more complex operations with tracked nodes.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/branches/immutableNodes@1580036 13f79535-47bb-0310-9956-ffa450edef68
Fixed compilation failures and failing test cases.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/branches/immutableNodes@1580037 13f79535-47bb-0310-9956-ffa450edef68