Added FileLocationStrategy interface.

This interface will be used for making the process of resolving files
customizable.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1525394 13f79535-47bb-0310-9956-ffa450edef68
Added ProvidedURLLocationStrategy.

This is a simple FileLocationStrategy implementation which checks whether the
passed in FileLocator already has a URL set. In this case, the file can be
accessed directly.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1525395 13f79535-47bb-0310-9956-ffa450edef68