Fixed #20794 -- Documented changes to validate_email

4e2e8f39d changed the way validate_email behaves for foo@localhost
email addresses, but wasn't listed in the release notes.
Fixed #14300 -- Fixed initial SQL location if models is a package.

Thanks al_the_x for the report and fheinz for the draft patch.
Fixed typo in Custom management commands documentation.
Merge pull request #1395 from funkbit/master

Fixed typo in Custom management commands documentation.
Fixed #19941 -- Modified runtests.py to make running the tests easier.

1. Automatically use tests/../django as the Django version.
2. If settings aren't provided through --settings or DJANGO_SETTINGS_MODULE)
   then use test_sqlite.
Fixed #20766 -- Deprecated FastCGI support.
Fixed #18168 -- clarified precedence of validation

any choices set by formfield_for_choice_field are still subject
to model validation of the model field's choices attribute
Fixed #20792 -- Corrected DISALLOWED_USER_AGENTS docs.

Thanks simonb for the report.
Fixed ._meta.pk_index() virtual field failure
Fixed #18315 -- Documented QueryDict.popitem and QueryDict.pop

Thanks gcbirzan for the report.
Fixed #20679 -- Corrected CachedFilesMixin.post_process docstring.

Thanks bmispelon for the report.
Fixed #20769 -- Added "Python compatibility" section to the 1.6 release notes.
Added versionadded directive missing from b7bd708.
Fixed handling of template loader tests.

Previously, the CachedLoaderTests were never run at all.
Fixed #20625 -- Chainable Manager/QuerySet methods.

Additionally this patch solves the orthogonal problem that specialized
`QuerySet` like `ValuesQuerySet` didn't inherit from the current `QuerySet`
type. This wasn't an issue until now because we didn't officially support
custom `QuerySet` but it became necessary with the introduction of this new
feature.

Thanks aaugustin, akaariai, carljm, charettes, mjtamlyn, shaib and timgraham
for the reviews.
Fixed related model lookup regression

It has been possible to use models of wrong type in related field
lookups. For example pigs__in=[a_duck] has worked. Changes to
ForeignObject broke that.

It might be a good idea to restrict the model types usable in lookups.
This should be done intentionally, not accidentally and without any
consideration for deprecation path.
Updated contrib.admin to use Email/URLInputs; refs #16630
Fixed #20805 -- Removed an extra colon beside checkboxes in the admin.

Thanks CollinAnderson for the report.
Fixed #18511 -- Cleaned up admin password reset template titles.
Fixed #18404 -- Added test for AppStaticStorage with non ascii path

(bug was already fixed in #19357)