Refs #7261 -- Made strings escaped by Django usable in third-party libs.

The changes in mark_safe and mark_for_escaping are straightforward. The
more tricky part is to handle correctly objects that implement __html__.

Historically escape() has escaped SafeData. Even if that doesn't seem a
good behavior, changing it would create security concerns. Therefore
support for __html__() was only added to conditional_escape() where this
concern doesn't exist.

Then using conditional_escape() instead of escape() in the Django
template engine makes it understand data escaped by other libraries.

Template filter |escape accounts for __html__() when it's available.
|force_escape forces the use of Django's HTML escaping implementation.

Here's why the change in render_value_in_context() is safe. Before Django
1.7 conditional_escape() was implemented as follows:

    if isinstance(text, SafeData):
        return text
    else:
        return escape(text)

render_value_in_context() never called escape() on SafeData. Therefore
replacing escape() with conditional_escape() doesn't change the
autoescaping logic as it was originally intended.

This change should be backported to Django 1.7 because it corrects a
feature added in Django 1.7.

Thanks mitsuhiko for the report.

mark_safe and mark_for_escaping should have been kept similar.

On Python 2 this change has no effect. On Python 3 it fixes the use case
shown in the regression test for mark_for_escaping, which used to raise
a TypeError. The regression test for mark_safe is just for completeness.

Thanks zimnyx for the report and Simon Charette, Tim Graham for
the reviews.

Added functions and tests
Added docs and more tests
Added TextField converter to mysql backend
Aliased Value as V in example docs and tests
Removed unicode_compatible in example
Fixed console emulation in examples

sqlall will be removed in Django 1.9, so now's a good time to remove
its usage where it's not important.

Initial SQL data will be removed in Django 1.9 so changes to it
aren't relevant.

Co-Authored-By: Rocky Meza <rmeza@fusionbox.com>

Thanks Mithos for the report and patch.

Refs #23866.

Refs #14515.

Refs #14394.

This removes the need to load django.test when not testing.

The migrations autodetector now issues AlterModelOptions operations for
Meta.managed changes instead of DeleteModel + CreateModel.

Thanks iambibhas for the report and Simon and Markus for review.

Also used schema editor in migrate to sync unmigrated apps (sync_apps).
Refs #22340. Thanks Tim Graham for the review.