Fix DisposableBean omission for Java DSL

http://stackoverflow.com/questions/43193858/tomcat-hangs-shutting-down-with-spring-integration-java-dsl

Using manual singleton registration doesn't provide automatic
`DisposableBean` registration

* Improve `IntegrationFlowBeanPostProcessor` to register `DisposableBean`  as well
* Improve `IntegrationFlowContext` to register `DisposableBean`  as well

spring-integration-core/src/test/java/org/springframework/integration/dsl/manualflow/ManualFlowTests.java

@@ -23,6 +23,7 @@ import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertThat;
+import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
 
 import java.util.Date;
@@ -34,6 +35,7 @@ import org.junit.runner.RunWith;
 
 import org.springframework.beans.factory.BeanCreationNotAllowedException;
 import org.springframework.beans.factory.BeanFactory;
+import org.springframework.beans.factory.DisposableBean;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.beans.factory.config.ConfigurableBeanFactory;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
@@ -127,6 +129,8 @@ public class ManualFlowTests {
 		ThreadPoolTaskScheduler taskScheduler = this.beanFactory.getBean(ThreadPoolTaskScheduler.class);
 		Thread.sleep(100);
 		assertEquals(0, taskScheduler.getActiveCount());
+
+		assertTrue(additionalBean.destroyed);
 	}
 
 	@Test
@@ -288,11 +292,14 @@ public class ManualFlowTests {
 
 	}
 
-	private final class BeanFactoryHandler extends AbstractReplyProducingMessageHandler {
+	private final class BeanFactoryHandler extends AbstractReplyProducingMessageHandler
+			implements DisposableBean {
 
 		@Autowired
 		private BeanFactory beanFactory;
 
+		private boolean destroyed;
+
 		@Override
 		protected Object handleRequestMessage(Message<?> requestMessage) {
 			Objects.requireNonNull(this.beanFactory);
@@ -304,6 +311,11 @@ public class ManualFlowTests {
 			this.beanFactory.getClass(); // ensure wiring before afterPropertiesSet()
 		}
 
+		@Override
+		public void destroy() throws Exception {
+			this.destroyed = true;
+		}
+
 	}
 
 }