Do not fallback to string on failure app, easier for debugging, closes #1587

lib/devise/failure_app.rb

@@ -64,7 +64,7 @@ module Devise
 
       if message.is_a?(Symbol)
         I18n.t(:"#{scope}.#{message}", :resource_name => scope,
-               :scope => "devise.failure", :default => [message, message.to_s])
+               :scope => "devise.failure", :default => [message])
       else
         message.to_s
       end

test/failure_app_test.rb

@@ -52,8 +52,8 @@ class FailureTest < ActiveSupport::TestCase
     end
 
     test 'uses the proxy failure message as symbol' do
-      call_failure('warden' => OpenStruct.new(:message => :test))
-      assert_equal 'test', @request.flash[:alert]
+      call_failure('warden' => OpenStruct.new(:message => :invalid))
+      assert_equal 'Invalid email or password.', @request.flash[:alert]
       assert_equal 'http://test.host/users/sign_in', @response.second["Location"]
     end