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)
Gave unique names to SpatialRefSysModels.

Prevented clashes in the app registry.

Fixed #22790. Thanks timo for the report.
Fixed #22777: Add dependency on through for autodetected M2M adds
Fix router_honored test to not close connection
Fixed #22487: Optional rollback emulation for migrated apps
Fix broken alias testing test
Converted Django scripts to argparse

Refs #19973.
Fixed formtools tests with Python 2

Fixes #19905 again.