Bug 126839 [DataBinding] IObservable refactoring
bundles/org.eclipse.jface.databinding/src/org/eclipse/jface/internal/databinding/beans/EditedCollectionRegistry.java
* @param collection the collection to no longer edit.
	 */
	public synchronized void unRegister(Object collection) {
		EditedCollection ec = (EditedCollection) editedCollections.get(collection);
		if (ec == null) {
			throw new IllegalArgumentException("Attept to unRegister an unregistered collection"); 
		}
		ec.count--;
		if (ec.count <= 0) {
			editedCollections.remove(collection);
		}
	}
	/**
	 * Method getUpdatable.  Returns an IUpdatableCollection given
	 * a collection to edit or null if an IUpdatableCollection
	 * cannot be made.  #register(Object collection) must have been
	 * previously called to register the specified collection.
	 * 
	 * @param collection The collection to edit.
	 * @return An IUpdatableCollection or null if none can be made.
	 */
	public IUpdatableCollection getUpdatable(Object collection) {
		EditedCollection ec = (EditedCollection) editedCollections.get(collection);
		if (ec == null) {
			throw new IllegalArgumentException("Attept to getUpdatable on an unregistered collection"); 
		}
		return ec.wrapper;
	}
}