Always bind with priv_user_dn if configured in validate as per Miguel Cabeça's patch.

Otherwise using validate for getting attributes (not authenticate eg. from cas)
would only bind with priv_user_dn when also searching for the dn was configured.


git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@976 44740490-163a-0410-bde0-09ae8108e29a