The macro was added for bpo-31338 in commit b2e57948

* bpo-21862: Add -m option to cProfile for profiling modules

It looks like this was copied from one of the previous tests, which did use it.

* bpo-31970: Reduce performance overhead of asyncio debug mode.

* fix doc for multiprocessing.connection.Client

The authenticate argument does not exist on either Client or Listener:
- https://github.com/python/cpython/blob/master/Lib/multiprocessing/connection.py#L483 (master)
- https://github.com/python/cpython/blob/3.6/Lib/multiprocessing/connection.py#L478 (3.6)
- https://github.com/python/cpython/blob/3.5/Lib/multiprocessing/connection.py#L478 (3.5)
- https://github.com/python/cpython/blob/3.4/Lib/multiprocessing/connection.py#L487 (3.4)
The documentation also claimed that these functions will call `current_process().auth_key`, for which I could find no evidence in the code. I rewrote the documentation to reflect the actual behavior.

Also made some small changes to vary sentence structure.

By accident the size of the empty dict keys object matched the
size of values array.

Few bytes at the begin and at the end of the reallocated blocks, as well
as the header and the trailer, now are erased before calling realloc()
in debug build.  This will help to detect using or double freeing the
reallocated block.

bpo-31764: Prevent a crash in sqlite3.Cursor.close() in case the Cursor object is uninitialized (#3958)

bpo-31770: Prevent a crash and refleaks when calling sqlite3.Cursor.__init__() more than once (#3968)

blocksize was hardcoded to 8192, preventing efficient upload when using
file-like body. Add blocksize argument to __init__, so users can
configure the blocksize to fit their needs.

I tested this uploading data from /dev/zero to a web server dropping the
received data, to test the overhead of the HTTPConnection.send() with a
file-like object.

Here is an example 10g upload with the default buffer size (8192):

$ time ~/src/cpython/release/python upload-httplib.py 10 https://localhost:8000/
Uploaded 10.00g in 17.53 seconds (584.00m/s)

real	0m17.574s
user	0m8.887s
sys	0m5.971s

Same with 512k blocksize:

$ time ~/src/cpython/release/python upload-httplib.py 10 https://localhost:8000/
Uploaded 10.00g in 6.60 seconds (1551.15m/s)

real	0m6.641s
user	0m3.426s
sys	0m2.162s

In real world usage the difference will be smaller, depending on the
local and remote storage and the network.

See https://github.com/nirs/http-bench for more info.

MemoryError raised when normalizing a RecursionError raised during exception normalization now not always causes a fatal error.

While technically a purely internal change, bpo-31845 was
a fairly significant externally visible bug caused by
these changes (environment variable based configuration
was being ignored due to a change in the relative order
of reading the environment and reading command line settings,
and the test suite was only testing the command line options)

Hence this note to essentially say "If you see odd startup
problems in 3.7 that you've never seen in previous releases,
it's probably our fault, so let us know, and we'll fix it".

This speeds up it to 20-40%.

* bpo-21423: Add an initializer argument to {Process,Thread}PoolExecutor

* Fix docstring