Ensure e-mail headers are binary type

Review Request #7612 — Created Aug. 26, 2015 and submitted — Latest diff uploaded

Information

Djblets
master

Reviewers

String literals are unicode by default so including headers from string
literals will result in unicode headers, which will result in unhappy
e-mails. We now ensure that e-mail headers are added to messages as a
binary type.

Unit tests have been updated to be more thorough about checking for
error states.

Ran unit tests.