Introduce AnnotationAwareOrderComparator#INSTANCE

Prior to this change, the INSTANCE constant one could refer to on
AnnotationAwareOrderComparator actually referred to the constant
declared in the OrderAwareComparator superclass. Thus
AnnotationAwareOrderComparator#INSTANCE did not actually return an
AnnotationAwareOrderComparator but an OrderAwareComparator instead. This
commit introduces a dedicated constant on AnnotationAwareOrderComparator
to avoid this glitch.

Issue: SPR-10038

spring-core/src/main/java/org/springframework/core/annotation/AnnotationAwareOrderComparator.java

 /*
- * Copyright 2002-2006 the original author or authors.
+ * Copyright 2002-2012 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.
@@ -27,12 +27,15 @@ import org.springframework.core.Ordered;
  * annotation value (if any).
  *
  * @author Juergen Hoeller
+ * @author Oliver Gierke
  * @since 2.0.1
  * @see org.springframework.core.Ordered
  * @see Order
  */
 public class AnnotationAwareOrderComparator extends OrderComparator {
 
+	public static AnnotationAwareOrderComparator INSTANCE = new AnnotationAwareOrderComparator();
+
 	@Override
 	protected int getOrder(Object obj) {
 		if (obj instanceof Ordered) {

spring-core/src/test/java/org/springframework/core/annotation/AnnotationAwareOrderComparatorTests.java

+/*
+ * Copyright 2012 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 org.springframework.core.annotation;
+
+import static org.hamcrest.CoreMatchers.*;
+import static org.junit.Assert.*;
+
+import org.junit.Test;
+
+/**
+ * Unit tests for {@link AnnotationAwareOrderComparator}.
+ * 
+ * @author Oliver Gierke
+ */
+public class AnnotationAwareOrderComparatorTests {
+
+	@Test
+	public void instanceVariableIsAnAnnotationAwareOrderComparator() {
+		assertThat(AnnotationAwareOrderComparator.INSTANCE, is(instanceOf(AnnotationAwareOrderComparator.class)));
+	}
+}