* bpo-6532: Make the thread id an unsigned integer.

From C API side the type of results of PyThread_start_new_thread() and
PyThread_get_thread_ident(), the id parameter of
PyThreadState_SetAsyncExc(), and the thread_id field of PyThreadState
changed from "long" to "unsigned long".

* Restore a check in thread_get_ident().

* Provide socket.TCP_NOTSENT_LOWAT
* New TCP option available on recent MacOS and Linux.
* Document addition of TCP_NOTSENT_LOWAT

Use --short form of git hash.  Use output from "git describe" for tag.

Expected outputs:
1. previous hg
2. previous git
3. updated git

Release (tagged) build:
1. Python 3.7.0a0 (v3.7.0a0:4def2a2901a5, ...
2. Python 3.7.0a0 (v3.7.0a0^0:05f53735, ...
3. Python 3.7.0a0 (v3.7.0a0:05f53735, ...

Development build:
1. Python 3.7.0a0 (default:41df79263a11, ...
2. Python 3.7.0a0 (master:05f53735, ...
3. Python 3.7.0a0 (heads/master-dirty:05f53735, ...

"dirty" means the working tree has uncommitted changes.
See "git help describe" for more info.

`NotImplentedError` --> `NotImplementedError`

This reverts commit 02371e0e.

From Shifted Dxit -> Shifted Exit in Doc/library/curses.rst

The $CXX environment variable is not exported under the 'c' language on Travis.

Based on patch by Vajrasky Kok.

Added the documentation for PyUnicode_Translate().

This will eliminate one of the builds in Travis, allowing for CI overall to complete faster.

The module is implicitly tested through test_urllib.

Initial patch by Vajrasky Kok.

Many metaclasses in the standard library don't play nice with
__init_subclass__. This bug makes ABCMeta in particular with
__init_subclass__, which is an 80/20 solution for me personally.
AFAICT, a general solution to this problem requires updating all
metaclasses in the standard library to make sure they pass **kwargs to
type.__new__, whereas this PR only fixes ABCMeta. For context, see
https://bugs.python.org/issue29581.

* added a test combining ABCMeta and __init_subclass__
* Added NEWS item

See https://github.com/python/cpython/pull/201#discussion_r103229425.

* Add _PyObject_HasFastCall()
* partial_call() now avoids temporary tuple to pass positional
  arguments if the callable supports the FASTCALL calling convention
  for positional arguments.
* Fix also a performance regression in partial_call() if the callable
  doesn't support FASTCALL.

Call abs_paths() only if removeduppaths() changed sys.path