Allow for overriding of computeTransactionAttribute

Issue: SPR-13246

spring-tx/src/main/java/org/springframework/transaction/interceptor/AbstractFallbackTransactionAttributeSource.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.
@@ -131,7 +131,7 @@ protected Object getCacheKey(Method method, Class<?> targetClass) {
 	 * {@link #getTransactionAttribute} is effectively a caching decorator for this method.
 	 * @see #getTransactionAttribute
 	 */
-	private TransactionAttribute computeTransactionAttribute(Method method, Class<?> targetClass) {
+	protected TransactionAttribute computeTransactionAttribute(Method method, Class<?> targetClass) {
 		// Don't allow no-public methods as required.
 		if (allowPublicMethodsOnly() && !Modifier.isPublic(method.getModifiers())) {
 			return null;