Added a mechanism to perform a bulk change without intermediate save().

This allows us to define more setter methods on configuration values, which in turn improves the ability to make programatic changes to the configuration, which in turn improves testability.

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@11515 71c3de6d-444a-0410-be80-ed276b4c234a