[CONFIGURATION-427] Support saving of arrays.

Arrays added to a XMLPropertyListConfiguration are now handled in a special way
so that their storage format is adapted. Thanks to Ho-jin Lee for the solution
proposal.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1635293 13f79535-47bb-0310-9956-ffa450edef68
[CONFIGURATION-427] Updated changes.xml.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1635294 13f79535-47bb-0310-9956-ffa450edef68