Avoid further 'type mismatch' errors in ExtendedBeanInfo

This change fixes further cases under JDK 6 in which setting a bridged
(e.g. String-returning) read method can conflict with an existing
corresponding bridge write method that accepts an Object parameter.

This appears to be a implementation difference between JDKs 6 and 7,
where the JDK 6 Introspector adds bridge methods and JDK 7 does not.

The solution here is to consistently null-out any existing write method
before setting the read method. We were doing this elsewhere in
ExtendedBeanInfo already, but these two changes make the approach
consistent throuhout.

Issue: SPR-8806

spring-beans/src/main/java/org/springframework/beans/ExtendedBeanInfo.java

@@ -301,6 +301,7 @@ class ExtendedBeanInfo implements BeanInfo {
 			}
 		}
 		else {
+			pd.setWriteMethod(null);
 			pd.setReadMethod(readMethod);
 			try {
 				pd.setWriteMethod(writeMethod);
@@ -310,6 +311,7 @@ class ExtendedBeanInfo implements BeanInfo {
 				// fall through -> add property descriptor as best we can
 			}
 			if (pd instanceof IndexedPropertyDescriptor) {
+				((IndexedPropertyDescriptor)pd).setIndexedWriteMethod(null);
 				((IndexedPropertyDescriptor)pd).setIndexedReadMethod(indexedReadMethod);
 				try {
 					((IndexedPropertyDescriptor)pd).setIndexedWriteMethod(indexedWriteMethod);