Bug 287103 [CommonNavigator] contentServiceLabelProvider doesn't properly implement overrides
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/internal/navigator/extensions/NavigatorContentDescriptorManager.java
overriddenDescriptor.getOverriddingExtensions().add(
							descriptor);
					descriptor.setOverriddenDescriptor(overriddenDescriptor);
					/*
					 * the always policy implies this is also a top-level
					 * extension
					 */
					if (descriptor.getOverridePolicy() == OverridePolicy.InvokeAlwaysRegardlessOfSuppressedExt) {
						if (Policy.DEBUG_EXTENSION_SETUP) {
							System.out.println(descriptor + " is first class"); 
						}
						firstClassDescriptorsMap.put(descriptor.getId(),
								descriptor);
						firstClassDescriptorsSet.add(descriptor);
					}
				} else {
					NavigatorPlugin.logError(0,
							"Invalid suppressedExtensionId (\"" 
									+ descriptor.getSuppressedExtensionId()
									+ "\" specified from " 
									+ descriptor.getContribution()
											.getPluginId()
									+ ". No extension with matching id found.", 
							null);
				}
			}
		}
	}
	private ImageRegistry getImageRegistry() {
		if (imageRegistry == null) {