bug#23068: 25.1.50; unix socket address in abstract namespace

[Mark Oteiza]

For the wishlist: teach emacs how to handle unix domain sockets with
an abstract address.  For instance, connecting to an abstract address
might look like:

  (make-network-process
   :name "dog" :buffer " *woof*"
   :service "\0sock" :family 'local)

the salient part being that the first element of the address is a null
byte. unix(7) has details.

In GNU Emacs 25.1.50.1 (x86_64-unknown-linux-gnu, X toolkit, Xaw scroll bars)
 of 2016-03-19 built on duoteque
Repository revision: 326fff41fa9f674d80be00b5c97c44f8043bbace
Configured using:
 'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
 --localstatedir=/var --without-gconf --with-modules
 --with-x-toolkit=lucid 'CFLAGS=-march=x86-64 -mtune=generic -O2 -pipe
 -fstack-protector-strong --param=ssp-buffer-size=4 -g
 -fvar-tracking-assignments -g -fvar-tracking-assignments'
 CPPFLAGS=-D_FORTIFY_SOURCE=2
 LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro'

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS NOTIFY
ACL GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS
LUCID X11 MODULES