Reflects behavior changes in PEP 495 (Local Time Disambiguation).

Fixed #26830 -- Prevented the 'with' templatetag from resetting the cycle variable to its initial state.

Refs #26830 -- Added a test for a named cycle template tag inside an ifchanged block and a for loop.

Fixed #27041 -- Documented that built-in middleware are compatible with MIDDLEWARE and MIDDLEWARE_CLASSES.

The spec refers to it as a 'directive' rather than a 'tag':
https://tools.ietf.org/html/rfc6797#section-6.1.2

After https://hg.python.org/cpython/rev/4ea79767ff75/,
test_strips_underscore_headers fails with:
'Stub' object has no attribute 'sendall'.

As makemessages uses several settings for proper run (FILE_CHARSET,
LOCALE_PATHS, MEDIA_ROOT, and STATIC_ROOT), we should require settings
configuration for this command.

Thanks Tim for the review.

This removes the need for some inner imports.

Thanks Gavin Wahl for the report, and Tim Graham for the review.

The test now also checks whether the sent message's attachment has the expected
name, content and mime type.

Fixed #27026 -- Fixed state initialization of bulk_create() objects if can_return_ids_from_bulk_insert.

* Added the index name to its deconstruction.
* Added indexes to sqlite3.schema._remake_table() so that indexes
  aren't dropped when _remake_table() is called.

Thanks timgraham & MarkusH for review and advice.