Merge BeanWrapperImpl and DirectFieldAccessor

`BeanWrapperImpl` and `DirectFieldAccessor` are two
`ConfigurablePropertyAccessor` implementations with different features
set.

This commit harmonizes the two implementations to use a common base class
that delegates the actual property handling to the sub-classes:

* `BeanWrapperImpl`:  `PropertyDescriptor` and introspection utilities
* `DirectFieldAccessor`: reflection on `java.lang.Field`

Issues: SPR-12206 - SPR-12805

spring-beans/src/test/java/org/springframework/beans/DirectFieldAccessorTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 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.
@@ -23,27 +23,29 @@ import org.springframework.tests.sample.beans.TestBean;
 import static org.junit.Assert.*;
 
 /**
- * Unit tests for {@link DirectFieldAccessor}
+ * Specific {@link DirectFieldAccessor} tests.
  *
  * @author Jose Luis Martin
  * @author Chris Beams
+ * @@author Stephane Nicoll
  */
 public class DirectFieldAccessorTests extends AbstractConfigurablePropertyAccessorTests {
 
 	@Override
-	protected ConfigurablePropertyAccessor createAccessor(Object target) {
+	protected DirectFieldAccessor createAccessor(Object target) {
 		return new DirectFieldAccessor(target);
 	}
 
+
 	@Test
 	public void withShadowedField() throws Exception {
 		@SuppressWarnings("serial")
-		TestBean tb = new TestBean() {
+		TestBean target = new TestBean() {
 			@SuppressWarnings("unused")
 			StringBuilder name = new StringBuilder();
 		};
 
-		DirectFieldAccessor dfa = new DirectFieldAccessor(tb);
+		DirectFieldAccessor dfa = createAccessor(target);
 		assertEquals(StringBuilder.class, dfa.getPropertyType("name"));
 	}
 

spring-beans/src/test/java/org/springframework/tests/sample/beans/TestBean.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2015 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.
@@ -38,6 +38,7 @@ import org.springframework.util.ObjectUtils;
  *
  * @author Rod Johnson
  * @author Juergen Hoeller
+ * @author Stephane Nicoll
  * @since 15 April 2001
  */
 public class TestBean implements BeanNameAware, BeanFactoryAware, ITestBean, IOther, Comparable<Object> {
@@ -58,6 +59,8 @@ public class TestBean implements BeanNameAware, BeanFactoryAware, ITestBean, IOt
 
 	private boolean jedi;
 
+	private ITestBean spouse;
+
 	protected ITestBean[] spouses;
 
 	private String touchy;
@@ -113,7 +116,7 @@ public class TestBean implements BeanNameAware, BeanFactoryAware, ITestBean, IOt
 	}
 
 	public TestBean(ITestBean spouse) {
-		this.spouses = new ITestBean[] {spouse};
+		this.spouse = spouse;
 	}
 
 	public TestBean(String name, int age) {
@@ -122,7 +125,7 @@ public class TestBean implements BeanNameAware, BeanFactoryAware, ITestBean, IOt
 	}
 
 	public TestBean(ITestBean spouse, Properties someProperties) {
-		this.spouses = new ITestBean[] {spouse};
+		this.spouse = spouse;
 		this.someProperties = someProperties;
 	}
 
@@ -210,17 +213,17 @@ public class TestBean implements BeanNameAware, BeanFactoryAware, ITestBean, IOt
 
 	@Override
 	public ITestBean getSpouse() {
-		return (spouses != null ? spouses[0] : null);
+		return this.spouse;
 	}
 
 	@Override
 	public void setSpouse(ITestBean spouse) {
-		this.spouses = new ITestBean[] {spouse};
+		this.spouse = spouse;
 	}
 
 	@Override
 	public ITestBean[] getSpouses() {
-		return spouses;
+		return (spouse != null ? new ITestBean[]{spouse} : null);
 	}
 
 	public String getTouchy() {