in test_pathlib.

Purposefully designed to work from a specified directory in case
multiple file systems are used on the system.

Only possibly-controversial change: joinpath() was described as:

  "Calling this method is equivalent to indexing the path with each of
  the *other* arguments in turn."

'Indexing' is an odd word to use, because you can't subscript Path or
PurePath objects, so I changed it to "combining".

Also, attempt to reduce confusion in the glossary by not saying there are
different "types" of arguments and parameters.

asyncio: Pass cancellation from wrapping Future to wrapped Future. By Saúl Ibarra Corretgé (mostly).

class.

built-in loading; leads to a reload scenario where attributes get set
which are wrong after the test.