Don't hard-code class names when calling static methods

normalize_email should be called on the instance, not the class. This
has the same effect normally but is more helpful to subclassers. When
methods are called directly on the class, subclasses can't override
them.
Tweak caching decorators/utility functions xrefs.
Fixed #16436 -- Oracle defer_regress test failure

Oracle doesn't like grouping by TextField, so use CharFields instead in
models.
Merge pull request #1232 from fusionbox/normalize_email

Fixed #20531 -- Don't hard-code class names when calling static methods
Fixed #20511 -- Corrected link about isolation levels in databases docs

Thanks tinodb for the report.
Fixed #20515 - Clarified note regarding translator comments.

Thanks wim@ for the suggestion.
Fixed #20326 - Corrected form wizard get_form() example.

Thanks tris@ for the report.
Fixed #20166 - Corrected TEST_DEPENDENCIES example in testing docs.

Thanks czambran.
Fixed #18681 -- BaseModelAdmin.get_form and InlineModelAdmin.get_formset no longer bypass get_fieldsets

Thanks msopacua for the report.
Improved the usage message of the test command.
Fixed #20404 -- Added a keys() method to ContextList.

It's useful to be able to list all the (flattened) keys of a
ContextList, to help you figure out why the variable that's supposed
to be there is not.

No .values() or .items() added as the definition for those aren't clear.

The patch is Chris Wilson's patch from pull request 1065 with some
modifications by committer.
Fixed #18785 -- Added Test join trimming regression

The regression was caused by patch to ticket #15316 and was fixed by a
patch to #10790.
Fixed #18169 -- NoReverseMatch not silenced if from block.super
Fixed #18481 -- Wrapped request.FILES read error in UnreadablePostError

Thanks KyleMac for the report, André Cruz for the initial patch and
Hiroki Kiyohara for the tests.
Fixed #20543 - Typo in db model fields docs.

Thanks i.amber.jain@ for the report.
Fixed #20540 -- Added more translatable strings to contrib.admindocs

Thanks lborgav for the initial patch.
Updated contrib.admindocs translation template
Changed assertEquals -> assertEqual.
Added minor splitting optimization in django.utils.ipv6._unpack_ipv4
Fixed #20337 -- Clarified error message when database relation is not allowed.