Bug 274236 [CommonNavigator] Incorrect check for existence of item in contribution memory
The check in the NavigatorContentService.rememberContribution() should be containsKey(), not containsValue()
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/internal/navigator/NavigatorContentService.java
* 
	 * @param element
	 *            The element to forget.
	 */
	public void forgetContribution(Object element) {
		contributionMemory.remove(element);
	}
	
	/**
	 * @param element
	 * @return the remembered NavigatorContentDescriptor
	 */
	public NavigatorContentDescriptor getContribution(Object element)
	{
		NavigatorContentDescriptor desc = (NavigatorContentDescriptor) contributionMemory.get(element);
		contributionMemory.remove(element);
		return desc;
	}
	
	/**
	 * 
	 * @param element
	 *            The element contributed by the descriptor to be returned
	 * @return The descriptor that contributed the element or null.
	 * @see #findContentExtensionsByTriggerPoint(Object)
	 */
	public synchronized NavigatorContentDescriptor getSourceOfContribution(Object element) {
		if (element == null)
			return null;
		if (structuredViewerManager == null)