Fixed #3711, #6734, #12581 -- Bounded connection.queries.

Prevented unlimited memory consumption when running background tasks
with DEBUG=True.

Thanks Rob, Alex, Baptiste, and others.
Fixed #17238 -- Added source code links to docs using sphinx.ext.viewcode.

Thanks santiagobasulto for the suggestion.
Fixed #18314 -- Corrected request.build_absolute_uri() handling of paths starting with //

``HttpRequest.build_absolute_uri()`` now correctly handles paths starting with ``//``.
``WSGIRequest`` now doesn't remove all the leading slashes either,
because ``http://test/server`` and http://test//server`` aren't the same thing
(RFC2396).

Thanks to SmileyChris for the initial patch.
Made a test compatible with Python 2 and 3.
Fixed #17427 -- Removed dubious definition of connections equality.
Fixed test again. Refs #12581.
Fixed #6992 -- Improved error when middleware omits HttpResponse.

Thanks guettli for the report.
Simplified module_has_submodule on Python >= 3.3.

Stopped using the imp module on Python >= 3.3. Refs #21628.
Fixed #20815 -- Don't enforce unbuffered I/O on Python 3.

No test because this code is already deprecated (part of FastCGI support).
Tested pluralization of decimals.

Refs #16723.
Silenced some GIS deprecation warnings; refs #22384.
Fixed #22436: More careful checking on method ref'ce serialization
Fixed #22749: Making SQL management commands migration aware.
Fixed flake8 error.
Removed usage of deprecated django.utils.importlib.
Fixed #22750, #22248: Model renaming now also alters field FKs
Optimize is_protected_type slightly (used by force_text, which is used basically everywhere)