Django-extensions

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Fix boo-boo with release version in django_extensions/__init__.py

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Changes:

- Fix missing test case

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Changes:

- Tests: shell_plus, simple test for get_imported_objects

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Changes:

- Fix: mail_debug, regression in mail_debug for older Pythons
- Fix: shell_plus, SyntaxError on exec(), python compatibility
- Fix: ForeignKeyAutocompleteAdminMixin, use text/plain

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Changes:

- Fix: graph_models, fix json option
- Fix: runserver_plus, avoid duplicate messages logged to console
- Fix: mail_debug, python3 fix
- Improvement: sqldiff, basic support for array types in postgresql
- Improvement: runscript, handle import errors better
- Docs: updated documentation for model extensions

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The change to --no-startup/--use-pythonrc in `shell_plus` changes the
default behaviour to automatically load PYTHONSTARTUP and ~/.pythonrc.py
unless --no-startup is set.

Changes:

- Fix: pipchecker, fix up-to-date check for Github sha commits
- Fix: JSONField, fix handling to_python() for strings with tests
- Fix: print_settings, fix print_settings to receive positional args
- Improvement: shell_plus, update PYTHONSTARTUP / pythonrc handling to match Django
- Improvement: shell_plus, added new 1.11 features from django.db.models to shell_plus import list
- Improvement: runserver_plus, startup message now accounts for https
- Docs: jobs, improve documentation about jobs scheduling
- Docs: admin, add documentation for ForeignKeyAutocompleteStackedInline and ForeignKeyAutocompleteTabularInline
- Docs: fix typos