Added i18n-related URL mapper test for a mailing list report.
Fixed #18924 -- Made test.Client.logout send user_logged_out signal.

Thanks awsum for the suggestion and Pavel Ponomarev and
Florian Hahn for the patch.
Fixed #17927 -- Added initial values support for BaseGenericInlineFormSet

Thanks Fak3 for the suggestion.
Proofed the 1.6 release notes
PEP 8 cleanup
Fixed #20564 -- Generic relations exclude() regression

The patch for #19385 caused a regression in certain generic relations
.exclude() filters if a subquery was needed. The fix contains a
refactoring to how Query.split_exclude() and Query.trim_start()
interact.

Thanks to Trac alias nferrari for the report.
Fixed #19080 -- Fine-grained control over select_related in admin
Fixed #20502 (again) -- More i18n cache flush in tests

Thanks Timo Graham for noticing the failures.
Fixed #12337 - Honor ModelForm.Meta.exclude when saving ManyToManyFields.

Thanks margieroginski for the report.
Bumped verion numbers for 1.6a1.
Explained that timezone.now() always returns times in UTC.

The docs were ambiguous about the time zone for now(), leading people to
assume that it would be the current time zone rather that UTC.
Fixed #19925 - Added validation for REQUIRED_FIELDS being a list

Thanks Roman Alexander for the suggestion.
Update submitting-patches.txt

Few quick fixes to the terminology in order to match what is used on the Django Trac at the moment.
Allow build of translated documentation
Replaced a dict emulating a set with a set.
Update media.txt

Fixed typo: froms -> forms
Fixed #20567 - Documented BoundField.id_for_label.

Thanks littlepig for the suggestion.
Fixed #19875 - Added warnings regarding DEBUG=False and empty ALLOWED_HOSTS
Added runserver validation to detect if DEBUG=False and ALLOWED_HOSTS is empty.

Refs #19875.
Refactored file_storage tests to avoid depending on servers tests.