Fixed #21212 -- Documented the reverse name for OneToOneField.

Thanks bjb at credil.org for the report.
Cleaned formatting/comments in PasswordResetFormTest
Fixed #21291 -- Ensured inactive users cannot reset their passwords

Thanks kz26 for the report and the suggested fix. Refs #19758.
Removed unused local variables in tests.
Fixed #21283 -- Added support for migrations if models is a package.

Thanks Markus Holtermann for the report.
Added support for serializing class methods. - Refs #21290.

The new handling allows us to do away with the whitelisting that was
required to support date and datetime objects.
Fixed an I18N test class tearDown method.
Fixed #21288 -- Fixed E126 pep8 warnings
Fixed E227 pep8 warnings
Fixed #21253 -- PBKDF2 with cached HMAC key

This gives a 2x speed increase compared to the existing implementation.