Fixed #18967 -- Don't base64-encode message/rfc822 attachments.

Thanks Michael Farrell for the report and his work on the fix.
Import test case classes from their public API module.
Documentation - Noted that OneToOneField doesn't respect unique.

Added OneToOneField to the list of model fields for which the unique
argument isn't valid. (OneToOneFields are inherently unique, and if
the user supplies a value for unique it is ignored / overwritten.)
Fixed #20946 -- model inheritance + m2m failure

Cleaned up the internal implementation of m2m fields by removing
related.py _get_fk_val(). The _get_fk_val() was doing the wrong thing
if asked for the foreign key value on foreign key to parent model's
primary key when child model had different primary key field.
Fixed #12422 -- Don't override global email charset behavior for utf-8.

Thanks simonb for the report, Claude Paroz and Susan Tan for their work
on a fix.
Switched mail tests to SimpleTestCase.
Fixed a regression with get_or_create and virtual fields.

refs #20429

Thanks Simon Charette for the report and review.
Fixed docstring typo, thanks minddust.
Added myself to the committers list.
Merge pull request #1498 from evildmp/add-myself

Added Daniele Procida to the committers list.
Fixed #20949 -- Typo #2 in docstring