Code patch by Serhiy Storchaka

Issue #20791: copy.copy() now doesn't make a copy when the input is a bytes object.  Initial patch by Peter Otten.

Patch by Berker Peksag.

The signature and description of PyException_SetCause now use "cause"
rather than "ctx" to match the code.

This bug was of the major reasons for the release.

Patch by Sean Rodman.

str.encode, bytes.decode and bytearray.decode now use an
internal API to throw LookupError for known non-text encodings,
rather than attempting the encoding or decoding operation and
then throwing a TypeError for an unexpected output type.

The latter mechanism remains in place for third party non-text
encodings.

Backported changeset d68df99d7a57.

Patch by Arfrever Frehtes Taifersar Arahesis.

Original patches by A. Kuchling and G. Rees (#12691).

constructed examples and all but 7 of the test/test_*.py files (run with -ucpu)
pass. Remove those that fail the new test from the selection list.
Patch partly based on patches by G. Brandl (#8478) and G. Rees (#12691).

The decoder does not support partial decoding yet for this code page.

when compiled with VS 2010 or above.  Initial patch by Tabrez Mohammed.

exception raised by sys.exit is None when no code is given.

As suggested by Serhiy Storchaka.

Tkinter widgets to work in wantobjects=True mode.

OSError(22, 'Invalid argument') when writing input data into stdin, whereas
the process already exited.

and to modernize.  Patch by Gareth Rees.

Patch based on lines from Georg Brandl, Eric Snow, and Gareth Rees.

Replace it with correct logic that raises ValueError for bad input.
Issues #8478 and #12691 reported the incorrect logic.
Add an Untokenize test case and an initial test method.