Revert "Release 2.4.0"

This reverts commit de267e907c930a4cc7831d80b51091f2ad73e084.

Found an issue with staged release
Fix NPE issue with JSF/Portlet support
Fix bug in SerializableListDataModel

This is a follow-up on an earlier commit:
https://github.com/spring-projects/spring-webflow/commit/97cc86b7c1ecd3b5b229c37837a44ee6e901501f

Issue: SWF-1510