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.

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).

Also added the missing documentation for new new option.

Also add the missing TextWrapper.shorten method doc.

Also reflow mmap paragraph.

Issue #20637: Key-sharing now also works for instance dictionaries of subclasses.  Patch by Peter Ingebretson.

I'm documenting this new function, but I'm wondering if this will trigger
someone to think about whether or not this actually makes sense :)