Extracted invocations of the configuration's synchronizer into own methods.

This gives subclasses the opportunity to perform additional actions before or
after read/write operations - as long as they know what they do.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1479377 13f79535-47bb-0310-9956-ffa450edef68