Fixed #19070: urlize template filter raises exception in some cases

Thanks and at cloverfastfood dot com for the report.

Fixed #19318 -- Ensured that the admin's SimpleListFilter options can be displayed as selected even if the lookup's first element is not a string.

Thanks Aymeric Augustin for detecting this regression.

Fixed typo in ValuesQuerySet._as_sql docstring

Thanks gw 2012 at tnode com for the report.

Fixed #17050 -- Added some CSS class names to the admin index pages to facilitate per-app or per-model style customizations. Thanks to scytale for the report and to H0ff1 and thiderman for their work on the patch.

ISO formats are automatically appended to the list of input
formats. Kept only when it is specified in first position, as it
has a special meaning in localize_input.
Thanks Bojan Mihelac for the report.

Thanks gregplaysguitar at gmail.com for the report.

Thanks tim.bowden at mapforge.com.au for the report, Andreas Hug
for the patch and Anton Baklanov for the review.

PermissionDeniedBackendTest references User model.

Thanks markteisman at hotmail.com for the report.

Fixed typo in the 1.5* release notes. Thanks brutasse.

Thanks Craig de Stigter for the report and collaboration on the
patch.

Reverse o2o fields are now usable with defer.

Fixed #19374 -- Typo in docs/ref/models/instances.txt.

Thank-you Daniel Greenfeld and Scott Nixon.

Thanks colinkeenan for the suggestion.

The connection state is now initialized in get_new_connection().
Refs #19274.

There was an assumption that changing connection.settings_dict changed
also the settings.DATABASES values. This assumption is now gone.

Connection creation was done in db backend ._cursor() call. This
included taking a new connection if needed, initializing the session
state for the new connection and finally creating the connection.

To allow easier modifying of these steps in subclasses (for example to
support connection pools) the _cursor() now calls get_new_connection()
and init_connection_state() if there isn't an existing connection. This
was done for all non-gis core backends. In addition the parameters used
for taking a connection are now created by get_connection_params().

We should also do the same for gis backends and encourage 3rd party
backends to use the same pattern. The pattern is not enforced in code,
and as the backends are private API this will not be required by
documentation either.

Thanks m3wolf for the report and akaariai for reproducing the problem.

Fixed #17911 -- Ensure that admin readonly fields' display values are shown in change forms when the raw value is None.