Bug 287103 [CommonNavigator] contentServiceLabelProvider doesn't properly implement overrides
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/internal/navigator/extensions/NavigatorContentDescriptor.java
try {
				enablement = ElementHandler.getDefault().create(
						ExpressionConverter.getDefault(), children[0]);
			} catch (CoreException e) {
				NavigatorPlugin.log(IStatus.ERROR, 0, e.getMessage(), e);
			}
		} else if (children.length > 1) {
			throw new WorkbenchException(NLS.bind(
					CommonNavigatorMessages.Attribute_Missing_Warning,
					new Object[] {
							TAG_ENABLEMENT,
							id,
							configElement.getDeclaringExtension()
									.getNamespaceIdentifier() }));
		}
		contribution = new IPluginContribution() {
			public String getLocalId() {
				return getId();
			}
			public String getPluginId() {
				return configElement.getDeclaringExtension().getNamespaceIdentifier();
			}
		};
		children = configElement.getChildren(TAG_OVERRIDE);
		if (children.length == 0) {
			overridePolicy = OverridePolicy.get(OverridePolicy.InvokeAlwaysRegardlessOfSuppressedExt_LITERAL);
		} else if (children.length == 1) {
			suppressedExtensionId = children[0]
					.getAttribute(ATT_SUPPRESSED_EXT_ID);
			overridePolicy = OverridePolicy.get(children[0]