bpo-31733, bpo-31692: Document the new PYTHONSHOWREFCOUNT and
PYTHONSHOWALLOCCOUNT environment variables.

bpo-31692, bpo-19527:

* Add a new PYTHONSHOWALLOCCOUNT environment variable, similar to
  the Python 3 "-X showalloccount" option
* When Python is compiled with COUNT_ALLOCS, the new
  PYTHONSHOWALLOCCOUNT environment variable now has to be set to dump
  allocation counts into stderr on shutdown. Moreover, allocations
  statistics are now dumped into stderr rather than stdout.
* Add @test.support.requires_type_collecting decorator: skip test if
  COUNT_ALLOCS is defined
* Fix tests for COUNT_ALLOCS: decorate some methods with
  @requires_type_collecting
* test_sys.test_objecttypes(): update object type when COUNT_ALLOCS
  is defined

Add a new PYTHONSHOWREFCOUNT environment variable. In debug mode,
Python now only print the total reference count if PYTHONSHOWREFCOUNT
is set.

(cherry picked from commit de072100)

[2.7] bpo-31490: Fix an assertion failure in ctypes in case an _anonymous_ attr is defined only outside _fields_. (GH-3615) (#3952)

[2.7] bpo-31728: Prevent crashes in _elementtree due to unsafe cleanup of Element.text and Element.tail (GH-3924) (#3950)

Also remove an obsolete note about
backward compat with old Pythons.

Add a new _testcapi._read_null() function to crash Python in a
reliable way on s390x.

On s390x, ctypes.string_at(0) returns an empty string rather than
crashing.

(cherry picked from commit 28f71360)

(cherry picked from commit 9e7b9b21)

(cherry picked from commit a8ed1174)

when pass a string larger than 2 GiB.

Decrease memory requirements for Tcl's bigmem tests..
(cherry picked from commit 27c623c8)

[2.7] bpo-31478: Prevent unwanted behavior in _random.Random.seed() in case the arg has a bad __abs__() method (GH-3596) (#3845)

(cherry picked from commit e6f62f69)

(cherry picked from commit f4ea642c)

[2.7] bpo-31285: Don't raise a SystemError in warnings.warn_explicit() in case __loader__.get_source() has a bad splitlines() method. (GH-3219) (#3823)

(cherry picked from commit 91fb0afe)

* init commit, with initial tests for from_param and fields __set__ and __get__, and some additions to from_buffer and from_buffer_copy

* added the rest of tests and patches. probably only a first draft.

* removed trailing spaces

* replace ctype with ctypes in error messages

* change back from ctypes instance to ctype instance

(cherry picked from commit 1bea762d)

[2.7] bpo-31490: Fix an assertion failure in ctypes in case an _anonymous_ attr is defined only outside _fields_. (GH-3615) (#3780)

(cherry picked from commit 30b61b51)

[2.7] bpo-31311: Fix a SystemError and a crash in ctypes._CData.__setstate__(), in case of a bad __dict__. (GH-3254). (#3781)

(cherry picked from commit 57c2561c)

(cherry picked from commit d6238a76)

[2.7] bpo-30347: Stop crashes when concurrently iterate over itertools.groupby() iterators. (GH-1557). (#3772)

(cherry picked from commit c740e4fe)

(cherry picked from commit 0e950dd2)

Patch by Raymond Hettinger.

Non-regression tests for the Expat 2.2.3 UTF-8 decoder bug.

(cherry picked from commit e6d9fcbb)

Previously ensurepip would always report success, even if the
pip installation failed.

(cherry picked from commit 9adda0cd)

Use prefixed macro names for the `authoraddress` function, add T2A to the font encoding in LaTeX sources to support Cyrillic characters in the PDF documentation, and replace the deprecated `font_size` config option with `pointsize`.
(cherry picked from commit da9b4cfb)

(cherry picked from commit 19e4d934)

(cherry picked from commit da67e0d6)

Signed-off-by: Christian Heimes <christian@python.org>

[2.7] bpo-31471: Fix assertion failure in subprocess.Popen() on Windows, in case env has a bad keys() method. (GH-3580) (#3595)

This no-op change makes 2.7 more consistent with 3.x to ease comparison and backports.

(cherry picked from commit 1de4705d)

fork_wait.py tests now joins threads, to not leak running threads in
the background.

(cherry picked from commit c99d41f9)