In asyncio.locks.Lock.acquire(): Avoid deadlock when a cancelled future is in self._waiters. (Merge 3.5->3.6)

The @reap_threads decorator made the test wait (for up to 1 s) until
background threads have finished.  Calling join() with a timeout should be
equivalent.

Issue #27809: PyEval_CallObjectWithKeywords() doesn't increment temporary the
reference counter of the args tuple (positional arguments). The caller already
holds a strong reference to it.

Issue #27809: Helper function optimized to create an exception: use fastcall
whenever possible.

Modify:

* init_subclass()
* builtin___build_class__()

Fix also a bug in init_subclass(): check for super() failure.

Issue #27809. _PyObject_FastCallDict() now supports keyword arguments, and so
the args==NULL fast-path can also be used when kwargs is not NULL.

Modify:

* builtin_sorted()
* classmethoddescr_call()
* methoddescr_call()
* wrapperdescr_call()

* Rename nm to name
* PEP 7: add { ... } to if/else blocks

Issue #27809:

* Rename _PyFunction_FastCall() to _PyFunction_FastCallDict()
* Rename _PyCFunction_FastCall() to _PyCFunction_FastCallDict()
*  _PyFunction_FastCallDict() now supports keyword arguments

Issue #27809:

* Rename _PyObject_FastCall() function to _PyObject_FastCallDict()
* Add _PyObject_FastCall(), _PyObject_CallNoArg() and _PyObject_CallArg1()
  macros calling _PyObject_FastCallDict()

This was found by PVS-Studio:

V595 The 'def' pointer was utilized before it was verified
against nullptr. Check lines: 286, 292. pystate.c 286

Initial patch by Christian Heimes.

Use flush=True to try to get a warning which is missing in buildbots.

Use also f-string to make the code shorter.

* main.py: remove unused import
* runtest: simplify runtest_inner() parameters, reuse ns parameter

Issue #27128. When a Python function is called with no arguments, but all
parameters have a default value: use default values as arguments for the fast
path.

Issue #27539: Fix unnormalised Fraction.__pow__ result for negative exponent and base. Thanks Vedran Čačić.

According to PEP 249, cursor.description must be
available for any SELECT statements, such as those
that use CTEs.

Backported from https://github.com/ghaering/pysqlite/commit/f67fa9c898a4713850e16934046f0fe2cba8c44c

Additional test cases added by me.

have caused off-by-one-ulp results on certain platforms.