This reverts commit 468a15aa.

encoding='latin1' should be used for successful decoding.

Set MemoryError when appropriate, add missing failure checks,
and fix some potential leaks.

Replace os.popen() with subprocess.check_output() in the platform module:

* platform.uname() (its _syscmd_ver() helper function) now redirects
  stderr to DEVNULL.
* Remove platform.DEV_NULL.
* _syscmd_uname() and _syscmd_file() no longer catch AttributeError.
  The "except AttributeError:" was only needed in Python 2, when
  os.popen() was not always available. In Python 3,
  subprocess.check_output() is always available.

* bpo-34864: warn if "Prefer tabs when opening documents" set to "Always"

* add NEWS entry

* address code review comments

* address second code review comments

* Add entry for idlelib/NEWS.txt.

https://bugs.python.org/issue35434

The function is never imported and the implementation is actually buggy.
As `warnings.catch_warnings` is not imported here.

Join 3 pools in these tests:

* test.test_multiprocessing_spawn.WithProcessesTestPool.test_context
* test.test_multiprocessing_spawn.WithProcessesTestPool.test_traceback

This reverts commit 97bfe8d3.

Moreover, "python3 -m test test_eintr -v" now avoids redirecting
stdout/stderr to a pipe, the child process inherits stdout/stderr
from the parent.

Escape the \t and \n.
Follow up from https://github.com/python/cpython/pull/10814.

On macOS, platform.platform() now uses mac_ver(), if it returns a
non-empty release string, to get the macOS version rather than darwin
version.

Add a missing word `as` in `as well as an`.
Linkify `threading.Thread`.

select() calls are retried on EINTR (per PEP 475).  However, if a
timeout was provided and the deadline has passed after running the
signal handlers, rlist, wlist and xlist should be cleared since select(2)
left them unmodified.

When running test_bdb.py as a script, `import test_module` would be
importing the existing Lib/test/test_modules.py instead of the
tempcwd/test_module.py module which was dynamically created by
test_bdb.py itself.

* posixpath.expanduser() now returns the input path unchanged if
  the HOME environment variable is not set and pwd.getpwuid() raises
  KeyError (the current user identifier doesn't exist in the password
  database).
* Add test_no_home_directory() to test_site.

* bpo-31572: Get rid of PyObject_HasAttrString() in ctypes.

* Fix error handling for _pack_.

* Don't silence errors when look up in a dict.

* Use _PyObject_LookupAttrId().

* More changes.

platform.libc_ver() now uses os.confstr('CS_GNU_LIBC_VERSION') if
available and the *executable* parameter is not set. The default
value of the libc_ver() *executable* parameter becomes None.

Quick benchmark on Fedora 29:

python3 -m perf command ./python -S -c 'import platform; platform.libc_ver()'
94.9 ms +- 4.3 ms -> 33.2 ms +- 1.4 ms: 2.86x faster (-65%)

On Travis CI, FTP tests of test_urllib2net randomly fail with "425
Security: Bad IP connecting".

test.pythoninfo now also logs TRAVIS environment variable.

Only platform._syscmd_file() uses subprocess. Move subprocess import
inside this function to reduce the number of imports at Python
startup.

Remove also warnings import which is no longer needed.