Added a constant for the default file location strategy to FileLocatorUtils.

This strategy will be used if no specific strategy is provided in a
FileLocator. The default location strategy is a combined strategy which
simulates the algortihm used in Commons Configuration 1.x.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1527226 13f79535-47bb-0310-9956-ffa450edef68