Bug 282049 Pass old context value to ContextChangeEvent
We should provide the "old value" for add and remove context change events. Knowing the old value will help listeners make more informed update decisions (i.e., they can accurately determine if the change effects them or not).
bundles/org.eclipse.e4.ui.workbench/src/org/eclipse/e4/workbench/ui/internal/UISchedulerStrategy.java
* Returns the singleton UI scheduler instance
	 * 
	 * @return the UI scheduler instance
	 */
	public static ISchedulerStrategy getInstance() {
		return instance;
	}
	public boolean schedule(final IEclipseContext context, final IRunAndTrack runnable,
			final String name, final int eventType, final Object[] args) {
		final boolean[] result = new boolean[1];
		Realm realm = Realm.getDefault();
		if (realm == null)
			return false;
		realm.asyncExec(new Runnable() {
			public void run() {
				result[0] = runnable.notify(EclipseContextFactory.createContextEvent(context,
						eventType, args, name, null));
			}
		});
		
		return result[0];
	}
	public void schedule(Runnable runnable) {
		Realm realm = Realm.getDefault();
		if (realm == null)
			return;
		realm.asyncExec(runnable);
	}
}