[1.2.X] Fixed #13494 -- Correctly concat an email subject prefix with a...

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

Backport from trunk (r14157).

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@14159 bcc190cf-cafb-0310-a4f2-bffc1f526a37