[commit by Simon]

- Update IDE dev tools plugin:
   - Prevent changes of plugin.xml and MANIFEST.MF.
   - While this avoid unwanted changes of these files (e.g.,
introduction of redundant dependencies), it also means that some
required modifications have to be performed manually now (in particular:
management of org.eclipse.emf.ecore.generated_package extension point)

- Date of IDE dev tools plugin has been bumped to date of first
implementation of this behavior (Aug 18, 2014).
Old version of plugin should be removed from Eclipse "dropins" directory.