title: Devise login validation failure
body: <p>I rails3.0.4 and devise installed with following users table </p>
  
  <pre>
  create_table "users", :force => true do |t|
      t.string   "login"
      t.string   "email"
      t.string   "crypted_password",         :null => false
      t.string   "password_salt",            :null => false
      t.string   "persistence_token",        :null => false
      t.string   "single_access_token",      :null => false
      t.string   "perishable_token",         :null => false
      t.datetime "created_at"
      t.datetime "updated_at"
      t.string   "database_authenticatable", :null => false
      t.string   "recoverable"
      t.string   "rememberable"
      t.string   "trackable"
      t.string   "reset_password_token"
    end
  </pre>
  
  <p>The users table was not created by devise but I added the necessary
  columns in migration.
  And following settings in config/initializers/devise.rb </p>
  
  <pre>config.authentication_keys = [ :email]</pre>
  
  <p>But every time I try to sign up as a new user it throws:</p>
  
  <pre>
    2 errors prohibited this user from being saved:
    Login is too short (minimum is 3 characters)
    Login should use only letters, numbers, spaces, and .-_@ please.
  </pre>
  
  <p>Any ideas why it could happen?  </p>