Added a method to FileLocatorUtils for obtaining a fully initialized FileLocator.

There are different ways to specify the file to be loaded depending on the
initialized fields of a FileLocator. If a file can be successfully located
based on this information, it makes sense to populate all the corresponding
member fields in a consistent way to point to this file.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1523799 13f79535-47bb-0310-9956-ffa450edef68