Added new FileLocator interface.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1460434 13f79535-47bb-0310-9956-ffa450edef68
Added an interface for passing a FileLocator.

This interface can be implemented by FileBased objects which needs access to
the current storage location on reading or writing.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1460435 13f79535-47bb-0310-9956-ffa450edef68