Fixed #18767 -- Fixed admin calendar for other locales than English.

Refactored openCalendar function from DateTimeShortcuts.js. Now, when
entered manually in the input field, the date will show up correctly on
the calendar for locales that don't use "-" for separator.

Thanks charettes for revivew and Alexey Boriskin for some of the patch.
Removed doc reference to removed HttpResponse.mimetype.
Corrected content_type parameter name in sitemap docs.

mimetype was deprecated in 1.5 per 11ec0253ab4cc926ab9e77619132cb398231ac33.
Fixed test failure on python 3.x.
Fixed #22971 -- Properly parsed RFC 2388 encoded headers

Thanks homm for the report, Cea Stapleton for patch improvements
and Ian Cordasco, Christian Schmitt and Tim Graham for the review.
Fixed #23265 -- Used system-specific encoding in runserver

Thanks SpaceFox for the report.
Fixed #21132 -- Removed the useless app_name argument to AdminSite.

Thanks MarkusH for the report and Florian for review.
Fixed #21579 -- Made LocaleMiddleware respect script prefix.

Thanks buettgenbach at datacollect.com for the report and patch.
Fixed #23260: Added generator support to defaultfilters.unordered_list.
Fixed #23291 -- Don't add Unicode varname/value to environment.

Windows doesn't like that and it causes 114 failures in the
admin_scripts tests with Python 2.x.
Fixed a grammar error in docs/ref/forms/api.txt.
Fixed #23224 - Documented EmailValidator.
Fixed #20133 -- Added summary to admin deletion confirmation pages.

Thanks jonash for the suggestion and initial patch.
Added some words to spelling_wordlist.
Fixed #23288: deconstruct() ignoring related_name
Complemented 1.6 release notes for 457c16d0d6

And accessorily added missing bits fixing #23293.
Forward port of 2cbafd814 from stable/1.7.x
Fixed typo in docs/howto/custom-model-fields.txt.
Fixed #23162 -- Renamed forms.Field._has_changed() to has_changed().
Fixed #23269 -- Deprecated django.utils.remove_tags() and removetags filter.

Also the unused, undocumented django.utils.html.strip_entities() function.
Fixed #23287 -- Updated error message for classonlymethod decorator.