FileBasedConfigurationBuilder now ensures that its FileLocator is fully defined.

Before actually loading the associated file, the locator's locate() method is
called. This ensures that all properties of the FileLocator pointing to the
file are initialized. This is important when saving the file: a fully
initialized FileLocator ensures that the correct output file is written.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1527238 13f79535-47bb-0310-9956-ffa450edef68