2012-06-13 Verion 0.5.2
- Change canonicalization defaults to work around issues with different
verification implementations <https://launchpad.net/bugs/939128>
- Fully fold DKIM-Signature on sign, and ignore FWS in b= value on verify
- Fix hashing problem while signing using sha1
- Trap NXDOMAIN exception with dnspython
- Other minor bug fixes