Thanks to Tim Graham for the review.

Thanks Daniele Procida for coauthoring.

Prevented LiveServerTestCase from stealing ports used by concurrent
processes on Windows.

Forward port of 59f3590c from stable/1.9.x.

Django's test suite often tries to load fixture files from apps that have
no fixtures at all. This creates a lot of unnecessary disabling and
enabling of constraints which can be expensive on some database.

To speed this up, loaddata now first checks if any fixture file matches.
If no fixture file is matched, then the command exits before disabling
and enabling of constraints is done.

The main benefit of this change is seen on MSSQL, where tests on
Django 1.8 run hours faster.

Thanks Thomas Güttler for motivating this addition.

Changed "dict.setdefault" to "if x in dict" pattern so that get_form() would not
be called unnecessarily, specifically in the case where FormMixin.form_invalid()
calls get_context_data() with the current form.

It looks like browsers have fixed the reported issue.

Fixed #25985 -- Updated signature of ModelAdmin.formfield_for_* to make request a positional argument.

Thanks Tim Graham for reviewing and contributing to the patch.
Refs #21113.

Forwardport of b51086d5 from stable/1.8.x

The use of predictable filenames in /tmp often leads to symlink attacks
so remove the most obvious use of them in the docs.