Corrected the order of operations in the test environment setup to ensure that...

Corrected the order of operations in the test environment setup to ensure that the original email backend can be restored. Thanks to koenb for the report.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@11718 bcc190cf-cafb-0310-a4f2-bffc1f526a37