Fixed another race condition with DynamicCombinedConfiguration.

Now all child configurations share a single Synchronizer with the parent
configuration. This ensures proper synchronization.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1489155 13f79535-47bb-0310-9956-ffa450edef68
Updated changes.xml.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1489156 13f79535-47bb-0310-9956-ffa450edef68