Fixed test for NodeAddData.

It was broken by the latest merge operation.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/branches/immutableNodes@1587010 13f79535-47bb-0310-9956-ffa450edef68
Reworked UnionCombiner to operate on ImmutableNode objects.

The class and its test class were adapted to be compatible with the changes
on the NodeCombinder base class.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/branches/immutableNodes@1587011 13f79535-47bb-0310-9956-ffa450edef68
Extended NodeModel interface for querying an in-memory representation.

A method was added for converting the data of the model into a structure of
ImmutableNode objects. This is necessary when multiple configuration sources
with different model implementations are to be combined.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/branches/immutableNodes@1587012 13f79535-47bb-0310-9956-ffa450edef68
Implemented getInMemoryRepresentation() in InMemoryNodeModel.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/branches/immutableNodes@1587013 13f79535-47bb-0310-9956-ffa450edef68