Why I consider this a bug rather than an API change: the API change was
to Message, which didn't used to return Headers unless you added them
yourself.  Now it does (for 8bit binary header input), so decode_header
needs to be able to handle them.

Algorithm and initial patch by Michael Henry.

Patch by Michael Henry.

The fix was already committed to 3.2, but I merged two small changes
recommended by Raymond while I was working on the 2.7 patch to ease
future merges.

Issue #10610: Document that int(), float(), and complex() accept numeric literals with the Nd property.

Issue #10610: Document that int(), float(), and complex() accept numeric literals with the Nd property.

(it's still very slow)