bpo-27584: New addition of vSockets to the python socket module (#2489)

bpo-27584: New addition of vSockets to the python socket module (#2489)

* bpo-27584: New addition of vSockets to the python socket module

Support for AF_VSOCK on Linux only

* bpo-27584: Fixes for V2

Fixed syntax and naming problems.
Fixed #ifdef AF_VSOCK checking
Restored original aclocal.m4

* bpo-27584: Fixes for V3

Added checking for fcntl and thread modules.

* bpo-27584: Fixes for V4

Fixed white space error

* bpo-27584: Fixes for V5

Added back comma in (CID, port).

* bpo-27584: Fixes for V6

Added news file.
socket.rst now reflects first Linux introduction of AF_VSOCK.
Fixed get_cid in test_socket.py.
Replaced PyLong_FromLong with PyLong_FromUnsignedLong in socketmodule.c
Got rid of extra AF_VSOCK #define.
Added sockaddr_vm to sock_addr.

* bpo-27584: Fixes for V7

Minor cleanup.

* bpo-27584: Fixes for V8

Put back #undef AF_VSOCK as it is  necessary when vm_sockets.h is not installed.