See PEP 3114. `next` is retained as an alias for Python 2.

The six addition has been borrowed from:
https://bitbucket.org/gutworth/six/changeset/733ef740

Fix #18062: Document best practices for choices in model fields.

In Python 3, the str type has an __iter__ attribute. Therefore, the
presence of an __iter__ attribute is not sufficient to distinguish
'standard' iterables (list, tuple) from strings.

Of course, __nonzero__ alias has been kept for Python 2 compatibility.

in the app directories template loader.

Add new security-policy documentation.

This formally describes our policies on reporting, notification and
disclosure of security issues, and provides a detailed explanation of
our full security-response process, for reference purposes.

This is necessary for the 'utils' tests to pass.

Based on Vinay Sajip's branch.

* Renamed smart_unicode to smart_text (but kept the old name under
  Python 2 for backwards compatibility).
* Renamed smart_str to smart_bytes.
* Re-introduced smart_str as an alias for smart_text under Python 3
  and smart_bytes under Python 2 (which is backwards compatible).
  Thus smart_str always returns a str objects.
* Used the new smart_str in a few places where both Python 2 and 3
  want a str.

Grammar fix in 1.5 release notes.