Fixed #23753 -- Added a suite of SQL Functions

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
Fixed #14180 -- Prevented unneeded index creation on MySQL-InnoDB

Thanks zimnyx for the report and Simon Charette, Tim Graham for
the reviews.
Forward-ported release note for 322560489
Fixed #24000 -- Corrected contrib.sites default site creation in a multiple database setup.
Fixed an inconsistency introduced in 547b1810.

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.
Fixed #23831 -- Supported strings escaped by third-party libs in Django.

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.
Added release notes for the last two commits.
Fixed #24057 -- Fixed typo in docs/howto/custom-lookups.txt.
Fixed #24056 -- Fixed syntax highlighting in topics/testing/tools.txt.
Simplified handling of a default value.
Renamed get_template_from_string to from_string.

The shorter name is just as explicit and, well, shorter.
Cleaned up the django.template namespace.

Since this package is going to hold both the implementation of the Django
Template Language and the infrastructure for Multiple Template Engines,
it should be untied from the DTL as much as possible within our
backwards-compatibility policy.

Only public APIs (i.e. APIs mentioned in the documentation) were left.
Imported BaseEngine from the DEP.

i18n is left aside for now.
Added initial support for loading template engines.
Added dummy template backend.
Added jinja2 template backend.
Added Django template backend.
Added basic tests for template backends.
Removed some uses of global APIs from django.template.loader.
Passed a reference to the current engine when instantiating Template.