Reworked test cases for reloading of combined configurations.

Because reloading is now handled by builders, tests related to reloading of
combined configurations have been removed from TestCombinedConfiguration.
A new test class has been added with corresponding tests for
ReloadingCombinedConfigurationBuilder.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1463692 13f79535-47bb-0310-9956-ffa450edef68
Changed test class: Only use methods from FileBased interface to load and save XMLConfiguration objects.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1463693 13f79535-47bb-0310-9956-ffa450edef68