Fixed invalid testing fixture
Oracle also treats NULLs as largests values when ordering.
Fixed #20933 -- Allowed loaddata to load fixtures from relative paths.
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.
Splitted QuerySet._clone() to _clone() and _pre_next_op()
Splitted Query.clone() to clone() and pre_next_op()
Added inplace querysets, used them in model.save()
Attempt to make some QuerySet operations faster by using inplace()
Renamed inplace -> _inplace