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.
Fixed #20860 -- Removed references to defunct chicagocrime.org
Added some Selenium tests for the admin raw id widget.
Added a note to the 1.6 release about the new `--keep-pot` option for `makemessages`.
Refs #17008.
Fixed a small formatting issue.
Fixed some intermittent Selenium test failures.
Fixed #20862 -- Updated startproject MIDDLEWARE_CLASSES in docs.

Thanks Keryn Knight.
Fixed #20859 - Clarified Model.clean() example.
Fixed #20832 -- Enabled HTML password reset email

Added optional html_email_template_name parameter to password_reset view
and PasswordResetForm.