Changed the key for storing file-based parameters in a parameters map.

Use a more simple key which makes it easier to create parameter maps manually,
e.g. in a Spring configuration file.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1606591 13f79535-47bb-0310-9956-ffa450edef68
Updated changes.xml for [CONFIGURATION-541].

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1606592 13f79535-47bb-0310-9956-ffa450edef68