LDAP authentication

[mogui]

I use lamernews internally at my company, so I needed it to be linked with the LDAP company accounts. Hop e is useful to others too.

By configuring in app_config.rb how to connect with an ldap server, username/password are checked against that directory. Registration and the forget password link are blocked and hided from the UI. Users are still stored the same way and are created the first time a user logged succesfull through ldap.