Updated 1.6.1 release notes

Partial forward port of e85baa813f.
Optimise admin images
Merge pull request #1931 from funkybob/admin-image-opt

Fixes #21455 - Optimise admin images

Every bit is sacred
Every bit is great
If a bit is wasted
God gets quite irate
Fixed #21404 -- Added session.set_expiry() note to 1.6 release notes.

Thanks pwr for the suggestion.
Fixed #21240 -- Added 1.5 release note for OneToOneField/select_related change.

Thanks marcin at sokrates.pl.
Added release note for TypedChoiceField coerce limitation

Thanks Elec for the report and Simon Charette for the review.
Refs #21397.
Fixed #21397 -- Re-added flexibility to TypedChoiceField coercion

Thanks Elec for the report and Simon Charette for the review.
Merged the signals and signals_regress test packages.

This patch also made the tests less likely to pollute the global state
in case of failure.
Added more internal links in the management command documentation.
Fixed #21457 -- Allowed fixture file name to contain dots

Thanks Keryn Knight for the report.
Fixed some Signal.disconnect calls from 058e434.

This would go unnoticed by the test suite because receivers are removed
automatically when they are garbage collected.

Changed all Signal.connect calls to hold strong references to ensure we
clean up after ourselves.
Fixed typo in topics/http/sessions.txt.
Fixed #15179 -- middlewares not applied for test client login()

Requests made with django.test.Client.login() and logout() respect
defaults defined in django.test.Client instantiation and are processed
through middleware.

Thanks to Loic for the reviews.
Fixed #21361 -- allowed access self.value() from SimpleListFilter lookup

Reviewed by Chris Medrela.
Fixed the base class note in the Date Views docs.
fixed typo in builtins.txt
Merge pull request #1943 from jantokhine/master

fixed typo in builtins.txt
Added more examples to the get_object_or_404 documentation.
Recommended setuptools in the reuseable app tutorial.

setuptools has merged with distribute.
Changed shortcuts from being a package to just being a module