The previous markup hijacked the abstract-base-classes glossary entry,
which resulted in the HTML linking to collections.abc when defining the
generic ABC concept.  Now the glossary links to the abc module.

I’m afraid my docstring is not as clear as it should be, but I can’t
find a concise way of describing what the code does.  Suggestions for
improvements welcome.

Keep a timeout of 1 hour for buildbots.

Also promote notices from distutils doc to deprecation boxes.

This removes the need to call flush manually in each test, except when
testing code that creates warning without checking them.

This updates the user guide to refer to Packaging instead of Distutils.
Some files still require an update.

document.

_check_dump_tracebacks_later() to avoid failures if the system is slow.

the file descriptor of a pipe closed in the parent process is valid in the
child process according to fstat(), but the mode of the file descriptor is
invalid, and read or write raise an error.

test.support.requires_mac_ver() is now a decorator, as suggested by Ezio
Melotti, and its docstring is fixed (linux_version => mac_ver).

descriptor of a pipe closed in the parent process is valid in the child process
according to fstat(), but the mode of the file descriptor is invalid, and read
or write raise an error.

Add also requires_mac_ver() decorator to test.support.

Add also linux_version() to __all__.