Revert dictionary item iteration in "libcython.py" to use ".iteritems()" instead of ".items()" since the first is implemented explicitly by "libpython.py".

Avoid generating empty tp_new() functions

Avoid generating empty tp_new() functions if we can copy the function pointer from the parent at init time.
See GH-1555.

Remove Cython/Includes/Deprecated

Avoid generating a tp_new() function for extension types that do not need their own one.

See #1555.

In test runner, change "compiling test" back to "compiling and running test" when executing a runnable test, which was accidentally lost before.

Reduce global state in FlowControl.py to see if it reduces the chance of reload problems (it's a compiled module which cannot be reloaded).

so it matches implementation :)

include: posix.mman += MAP_FAILED

include: posix.mman += mlock2, MLOCK_ONFAULT, MCL_ONFAULT

Import "Iterable" ABC class from "collections.abc" in Py3 instead of deprecated "collections" package.

Fix some "resource usage" warnings for unclosed process pipes when running in a CPython debug build.

Fix some "resource usage" warnings for unclosed files in tests when running in a CPython debug build.

mmap returns void* and indicates failure via MAP_FAILED that is defined
to be ((void *)-1). Every mmap call has to be checked for failure and
thus posix.mman with mmap, but without MAP_FAILED is not very useful.

We cannot declare MAP_FAILED as enum, because enum assumes int. However
Cython documentation says

	4. If the header file uses macros to define constants, translate
	   them into a normal external variable declaration. ...

	(https://cython.readthedocs.io/en/latest/src/userguide/external_C_code.html#referencing-c-header-files)

So add proper declaration for MAP_FAILED to make posix.mman.mmap usable.

mlock2 is Linux-specific version of mlock that accepts flags. The only
flag available so far is MLOCK_ONFAULT which asks to lock pages only at
the time when they are faulted in, not in the beginning. MCL_ONFAULT is
Linux-specific flag to mlockall which requests similar behaviour.

http://man7.org/linux/man-pages/man2/mlock2.2.html