Merged r12070 from trunk to 2.3-stable

not use assert_not_nil in Errors#[].

r7593 etc. replaced Rails2 Errors#on.
Rails3 Errors#[] always return array.
So, Rails3 Errors#[] is always not nil.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/branches/2.3-stable@12071 e93f8b46-1217-0410-a6f0-8f06a7374b81

test/unit/user_test.rb

@@ -366,7 +366,7 @@ class UserTest < ActiveSupport::TestCase
     u = User.new
     u.mail_notification = 'foo'
     u.save
-    assert_not_nil u.errors[:mail_notification]
+    assert_not_equal [], u.errors[:mail_notification]
   end
 
   context "User#try_to_login" do