SimpleSession serializes fields twice

org.apache.shiro.session.mgt.SimpleSession serializes fields twice - once via the 'writeObject' implementations' call to out.writeDefaultObject(), and again via the custom bitmask-based serialization that follows it.

The internal fields should be marked as transient to prevent this. out.writeDefaultObject should still be called for JVM security reasons, but SimpleSession's custom field-based serialization is more efficient so it should be retained. The solution is to mark all custom-serialized fields as transient.

Discussion thread here: http://mail-archives.apache.org/mod_mbox/shiro-user/201109.mbox/%3C4E81BCBD.8060909@metaphysis.net%3E