Fixed #18832 - Updated ModelForm example fields to match note below

Fixed a typo in the Python 3 compatibility docs.

Fixes #18245. Refs #3542.

Removed admin's swallowing of AttributeError (#16655, #18593, #18747)

During the new-admin changes, catching of AttributeError was added to
the admin.  This patch removes that as it's no longer possible to add a
value to a ModelAdmin that is not available.  Adding an attribute that
can not be called causes an ImproperlyConfigured exception to be raised.

Thanks mrmagooey for the draft patch.

Refs #16023.

Thanks Nick Martini for the patch.

Fixed #18928 - Tightened language in docs/README

Thanks Shabda Raaj for the draft patch.

Refs #17574.

* Stated upfront that the messages framework is enabled by default.
* Explained why FallbackStorage, despites its unattractive name, is the
  default and likely the most efficient message storage class.

Thanks Jeremy Dunck for the review.

Closes #17026 (again).

Trying to move most of the introductory example stuff up to the top and
pushing the reference bits further down.

Thanks Malcolm Tredinnick for the review.

Remove unused imports in tutorial 4. refs #18915

Updated text in tutorial 3 regarding removing unused import; refs #18915

Thanks kmike.

Closes #17452.

Fixed #12397 -- allow safe_join to work with the root file system path, which means you can have your root template or file upload path at this location. You almost certainly don't want to do this, except in *very* limited sandboxed situations.

After submitting ticket #18915, I noticed 2 additional occurrences of the issue. 

Removed many uses of bare "except:", which were either going to a) silence real issues, or b) were impossible to hit.

Ticket #17324 - Improve security docs with better CSRF explanation

clarify clean_<field> docs, ticket #18917

Fixed #17888 -- no longer silence exceptions inside of check_test. Thanks to brutasse for the patch.

Previous this used Python's builtin hash() function, which has never been guarnteed to be stable across implementations (CPython/Jython/etc.) or 32/64 bitness. However, this in practice it was stable. However, with the impending release of Python 3.3 hash randomizations is enabled by default, which would mean the index name changed between program invocations.