This action logs the current user into a given handler. If the
authentication is successful, a map is returned with the authentication
information and a session is created (if it not already exists).
If the authentication is not successful, the error information is stored
into the temporary context.
author: Carsten Ziegeler version: CVS $Id: LoginAction.java 433543 2006-08-22 06:22:54Z crossley $