(grafted from 4cb3ea76ce68efd52271e499647abbf0f8a2941f)

(grafted from 418ba3a0f090ac0e17a935b7cd5a63ea8263a914)

Patch by Eric Appelt.
(grafted from 78c8f450b84ca1864123ec487d363eb151f61a4a)

Issue #28147: Fix a memory leak in split-table dictionaries: setattr() must not
convert combined table into split table.

Patch written by INADA Naoki.
(grafted from 85be9dcc16a81d3ccd1f67b056255a7f206edd47)

The new dict implementation is not faster, but more compact.

Patch written by Brendan Donegan.
(grafted from 181453f9a0c424212f0f6ddca2b9065c15689d7c)

Initial patch by Mariatta Wijaya.
(grafted from 853e3f4d6cd98ac4590238bc1c60e40fd8ed3895)

(grafted from 25df9671663b5f8b1560d58d8842f9676f6dffc2)

(grafted from 4745d801cae2d57e3432313acd0b76b8b4cc9c75)

(grafted from d12bc674b74eee73365e38fad1f170ed3349bd59)

Patch by Serhiy Storchaka.

again.  But they still are deprecated and will be disabled in 3.7.

The fix for catch_warnings() is the issue #28835 (not the issue #28089).

Issue #28089: Fix a regression introduced in warnings.catch_warnings(): call
warnings.showwarning() if it was overriden inside the context manager.

Handling zero-argument super() in __init_subclass__ and
__set_name__ involved moving __class__ initialisation to
type.__new__. This requires cooperation from custom
metaclasses to ensure that the new __classcell__ entry
is passed along appropriately.

The initial implementation of that change resulted in abruptly
broken zero-argument super() support in metaclasses that didn't
adhere to the new requirements (such as Django's metaclass for
Model definitions).

The updated approach adopted here instead emits a deprecation
warning for those cases, and makes them work the same way they
did in Python 3.5.

This patch also improves the related class machinery documentation
to cover these details and to include more reader-friendly
cross-references and index entries.