Fixed #22030 -- Don't assume that all fields have a swappable_setting at...

With this pull request, request #878 should considered closed.

Thanks to nvie for the patch.

That method was introduced in 9db4271b.

Refs #21765.

Thanks to lee for the report.

Refs #21765.

Thanks to kezabelle for the quick report and to onjin
for providing the patch.

Thanks Marc Tamlyn for the suggestion.

Thanks to nedbatchelder for the report.

Commit 79558c78 cleaned up the (undocumented) interface of Resolver404
exception, which breaks compatibility with code messing with .args[0]
directly. Revert the cleanup part and simply leave the fix itself.

Thanks to mondone for fruitful colaboration.

Thanks brycenesbitt for the report.

Thanks to cjerdonek for the suggestion.

When django.core.urlresolvers.resolve was called from a view, failed
and the exception was propagated and rendered by technical_404_response,
the URL mentioned on the page was the current URL instead of the URL
passed to resolve().

Fixed by using the path attribute from the Resolver404 exception instead
of request.path_info. Also cleaned up the exceptions to use standard
named parameters instead of stuffing a dict in args[0]

Thanks tunixman for the report and Baptiste Mispelon and
Shai Berger for reviews.

Flatten a level of sublists before checking for duplicate fields.

When given sublists such as:

```python

class FooAdmin(admin.ModelAdmin):
    fields = ('one', ('one', 'two'))
```

The previous code did not correctly detect the duplicated 'one' field.

Thanks to jwa for the report.

Thanks apollo13: "reverse() shouldn't know about absolute/relative paths."

Change analyse (British) to analyze (American).

Now AddField actions appear in operations list before AlterUniqueTogether
actions.

Thanks to SmileyChris for the report.

Thanks Klemens Mantzos for the report and initial patch.

Thanks leahculver for the suggestion and Erik Romijn,
Simon Charette, and Marc Tamlyn for the reviews.

This fixes redirecting to relative URLs with django.shortcuts.redirect.

Thanks selwin for the suggestion.

Commit 4523fcd6 introduces _actions_icnt to the local scope,
which overrides the value set in the HTML.

The admin would incorrectly show selected rows in a change list
as "1 of undefined selected".