Added hint towards not using orm.hibernate3 classes with Hibernate 4

Issue: SPR-9365

spring-orm-hibernate4/src/main/java/org/springframework/orm/hibernate4/package-info.java

@@ -6,10 +6,13 @@
  *
  * <p>Contains an implementation of Spring's transaction SPI for local Hibernate transactions.
  * This package is intentionally rather minimal, with no template classes or the like,
- * in order to follow native Hibernate recommendations as closely as possible.
+ * in order to follow Hibernate recommendations as closely as possible. We recommend
+ * using Hibernate's native <code>sessionFactory.getCurrentSession()</code> style.
  *
  * <p><b>This package supports Hibernate 4.x only.</b>
  * See the {@code org.springframework.orm.hibernate3} package for Hibernate 3.x support.
+ * <b>Note:</b> Do not use HibernateTemplate or other classes from the hibernate3 package
+ * with Hibernate 4; this will lead to class definition exceptions at runtime.
  *
  */
 package org.springframework.orm.hibernate4;