title: Devise ldap authenticable does not lookup correctly
body: <p>I am trying to get user properties from ldap on rails + devise_ldap_authenticatable
  (devise_ldap_authenticatable 0.8.1, rails 3.2.14)</p>
  
  <p>Blow is my configuration</p>
  
  <p>devise.rb</p>
  
  <pre><code>config.ldap_logger = true
  config.ldap_create_user = true
  config.ldap_config = "#{Rails.root}/config/ldap.yml"
  </code></pre>
  
  <p>ldap.yml (./config/ldap.yml)</p>
  
  <pre><code>authorizations: &amp;AUTHORIZATIONS
   group_base: OU=Employee,OU=Person,DC=TEST,DC=AD
   required_groups:
    - CN=users,OU=Employee,OU=Person,DC=TEST,DC=AD
  
   require_attribute:
    objectClass: inetOrgPerson
    authorizationRole: postsAdmin
  
  development:
   host: 192.168.1.10
   port: 389
   attribute: CN
   base: OU=Employee,OU=Person,DC=TEST,DC=AD
   ssl: false
  </code></pre>
  
  <p>user.rb</p>
  
  <pre><code>devise :ldap_authenticatable, :registerable, revoerable, 
         :rememberable, :trackable, :validatable
  before_save :get_ldap_email
  
  def get_ldap_email
     self.email = Devise::LDAP::Adapter.get_ldap_param(self.username, "mail")
  end
  </code></pre>
  
  <p>and my LDAP(AD) status is</p>
  
  <pre><code>CN=12345678,OU=Employee,OU=Person,DC=TEST,DC=AD is exist
  and it has mail attribute =&gt; "12345678@test.com"
  </code></pre>
  
  <p>The Login process was good
  But It didn't get any properties</p>
  
  <p>log is ...</p>
  
  <pre><code>User Load (0.3ms)  SELECT `users`.* FROM `users` WHERE `users`.`username` = '12345678'    ORDER BY created_at DESC LIMIT 1
  LDAP: LDAP dn lookup: CN=12345678
  LDAP: LDAP search for login: CN=12345678
  LDAP: LDAP search yielded 0 matches
  LDAP: Authorizing user 12345678@test.ad
  LDAP: LDAP dn lookup: CN=12345678
  LDAP: LDAP search for login: CN=12345678
  LDAP: LDAP search yielded 0 matches
  </code></pre>
  
  <p>and</p>
  
  <pre><code>Devise::LDAP::Adapter.get_ldap_param(self.username, "mail")
  #It returns nil
  </code></pre>
  
  <p>Maybe the lookup address is wrong...
  (maybe CN=12345678,OU=Employee,OU=Person,DC=TEST,DC=AD is correct)</p>
  
  <p>How can i fix it?
  How can i get user properties? (ex: mail ...)</p>