Support ServletContextListener with Jetty 9

Call `context.getServletContext().setExtendedListenerTypes(true)` to
ensure that ServletContextListeners can be registered with Jetty 9.

Fixes gh-2058

spring-boot-samples/spring-boot-sample-jetty/src/main/java/sample/jetty/ExampleServletContextListener.java

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2012-2014 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package sample.jetty;
+
+import javax.servlet.ServletContextEvent;
+import javax.servlet.ServletContextListener;
+
+import org.springframework.stereotype.Component;
+
+/**
+ * Simple {@link ServletContextListener} to test gh-2058.
+ */
+@Component
+public class ExampleServletContextListener implements ServletContextListener {
+
+	@Override
+	public void contextInitialized(ServletContextEvent sce) {
+		System.out.println("*** contextInitialized");
+	}
+
+	@Override
+	public void contextDestroyed(ServletContextEvent sce) {
+		System.out.println("*** contextDestroyed");
+	}
+
+}