Fixed #13494 -- Correctly concat an email subject prefix with a translation...

Fixed #13494 -- Correctly concat an email subject prefix with a translation string. Thanks, hcarvalhoalves and Andi Albrecht.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14157 bcc190cf-cafb-0310-a4f2-bffc1f526a37