Thanks Tim Graham and Simon Charette for the reviews.

Previously, known related objects overwrote related objects loaded
though select_related. This could cancel the effect of select_related
when it was used over more than one level.

Thanks boxm for the bug report and timo for bisecting the regression.

Signed-off-by: Jason Myers <jason@jasonamyers.com>

Test models introduced for #10733 didn't contain default value for
a BooleanField(). Check command didn't like that -> check tests failed.

The bug was reported pre 1.1, and somewhere along the way it has been
fixed. So, this is tests only addition.

Should be unneeded with Python 2.7 and up.
Added some unicode_literals along the way.