Fixed IRC channel name in submitting-patches.txt.

The development channel is #django-dev.
Fixed #12008 -- Clarified relationship between template blocks and includes.

Thanks Daniele Procida for suggested wording.
Minor cleanup in the check_framework test package.
Fixed #23615 -- Validate that a Model instance's "check" attribute is a method.

The "check" name is a reserved word used by Django's check framework,
and cannot be redefined as something else other than a method, or the check
framework will raise an error.

This change amends the django.core.checks.model_check.check_all_models()
function, so that it verifies that a model instance's attribute "check"
is actually a method. This new check is assigned the id "models.E020".
Fixed #23667 -- Incorrect settings reference for language cookie.

Thanks jamesbeith for the report.
Fixed some intersphinx references.
Fixed #23649 -- Made Oracle test-db creation drop test-user earlier when needed

Checked database destruction for ORA-29857, which happens when objects of
some types are left over in an old test database (notably, such objects
are created by the GIS backend). When this happens, we can resolve the
issue by dropping the test-user (if we are allowed to).

An alternative approach, to just switch the order of creation (so that,
if the test user exists and can be dropped, it is always dropped before
the tablespace) was considered; but since the user creation depends on
the tablespace, this would necessitate separating the dropping of the user
from its creation -- a change I am reluctant to make.

Thanks Josh Smeaton and Tim Graham for reviews.