Patch by Christian Heimes, reviewed by Martin Panter.

Patch by SilengGhost.

Use a small stack allocated in the C stack for up to 5 iterator functions,
otherwise allocates a stack on the heap memory.

Issue #27809:

* PyObject_CallMethodObjArgs(), _PyObject_CallMethodIdObjArgs() and
  PyObject_CallFunctionObjArgs() now use fast call to avoid the creation of a
  temporary tuple
* Rename objargs_mktuple() to objargs_mkstack()
* objargs_mkstack() now stores objects in a C array using borrowed references,
  instead of storing arguments into a tuple

objargs_mkstack() uses a small buffer allocated on the C stack for 5 arguments
or less, or allocates a buffer in the heap memory.

Note: this change is different than the change 0e4f26083bbb, I fixed the test
to decide if the small stack can be used or not. sizeof(PyObject**) was also
replaced with sizeof(stack[0]) since the sizeof() was wrong (but gave the same
result).

Issue #27809:

* PyObject_CallMethodObjArgs(), _PyObject_CallMethodIdObjArgs() and
  PyObject_CallFunctionObjArgs() now use fast call to avoid the creation of a
  temporary tuple
* Rename objargs_mktuple() to objargs_mkstack()
* objargs_mkstack() now stores objects in a C array using borrowed references,
  instead of storing arguments into a tuple

objargs_mkstack() uses a small buffer allocated on the C stack for 5 arguments
or less, or allocates a buffer in the heap memory.

Use a small stack allocated in the C stack for up to 5 iterator functions,
otherwise allocates a stack on the heap memory.

Patch by Ivan Levkivskyi, docs by Neil Girdhar.

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()