Added CombinedLocationStrategy class.

This class allows the creation of a custom FileLocationStrategy based on other
"primitive" strategies. Arbitrary combinations can be created to adapt the
location algorithm to very specific requirements.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1525402 13f79535-47bb-0310-9956-ffa450edef68