Removed unused model option "admin"
Fixed #20667 - Removed discussion of DEBUG from tutorial.

Forward-port of 3493f18d78 from master.
Fixed #17519 -- Fixed missing SQL constraints to proxy models.

Thanks thibaultj for the report, jenh for the patch,
and charettes for the tests.
Fixed #18777 -- Localized form fields with as_text/as_hidden

Thanks croldan for the report.
Fixed #20838 -- Fixed Geodjango spatialrefsys test failure with postgis-2.0.3
Fixed #20786 -- Cleaned up docs/ref/exceptions.txt

Thanks Daniele Procida for the suggestion and edits.
Fixed #18681 -- GenericInlineModelAdmin.get_formset() no longer bypasses get_fieldsets().

Refs 23e1b59 which already fixed this issue for ModelAdmin and InlineModelAdmin.
Fixed LogEntry.get_admin_url() for non-existent models.

Regression introduced by [369b6fa]; refs #18169.
Fixed #18923 -- Corrected usage of sensitive_post_parameters in contrib.auth

Thanks Collin Anderson for the report.
Added missing request argument to example in URL dispatcher docs
Added ModelAdmin.get_search_fields.
Fixed #20822 -- Set content type of default error pages to 'text/html'.

Thanks Jimmy Song for the patch.
Fixed #20858 -- Removed erroneous import in tutorial 2.

Thanks AtomicSpark.
Moved get_search_results from BaseModelAdmin to ModelAdmin.

Refs #15961.
Deprecated SortedDict (replaced with collections.OrderedDict)

Thanks Loic Bistuer for the review.
Merge pull request #1432 from loic/modeladmin.get_search_results

Moved get_search_results from BaseModelAdmin to ModelAdmin.
Fixed #20855 -- Added documentation of current_app and extra_context params to django.contrib.auth views

refs #5298 and refs #8342
Introduced ModelAdmin.get_fields() and refactored get_fieldsets() to use it.

Refs #18681.

This also starts the deprecation of ModelAdmin.declared_fieldsets
Fixed a number of lint warnings, particularly around unused variables.
Fixed #20842 and #20845 - Added a note on order_by() and improved prefetch_related() docs.