Fixed SESBackedTest.

Fixed the SESBackendTest so that the test_send_mail() test passes.
The standard email module's message_from_string() function seems
to parse unicode objects entirely as the message body so I converted
the raw message unicode object to a string.
Merge remote-tracking branch 'hmarr/master' into fix-ses-backend
Add Python 2.6 back in with these changes
Merge branch 'fix-ses-backend'

Thanks @IanLewis for the fix!