Bug 299340 [CommonNavigator] Enable new CNF tests
Enable the contributed CNF tests, make minor test improvements.
tests/org.eclipse.ui.tests.navigator/src/org/eclipse/ui/tests/navigator/M12Tests.java
public M12Tests() {
		_navigatorInstanceId = TEST_CONTENT_M12_VIEW;
	}
	private void _initContent() {
		String[] EXTENSIONS = new String[] { COMMON_NAVIGATOR_RESOURCE_EXT,
		
				
				TEST_CONTENT_M12_M1_CONTENT, TEST_CONTENT_M12_M2_CONTENT };
		_contentService.bindExtensions(EXTENSIONS, false);
		_contentService.getActivationService().activateExtensions(EXTENSIONS,
				true);
	}
	/**
	 * Test that 2nd level extension isn't erroneously remembered as the source