bug#31636: 27.0.50; lockfile syntax searchable from info manual

[Brady Trainor]

I had hoped to find about files such as `/tmp/.#fileA` by searching in
the info manual for ".#". But I did not find such a string there, nor
via `apropos-documentation`.

If a user encounters such a file in a directory, I think it would lead
to good discoverability if a manual or docstring had some mention of the
string ".#", so that one might search for it.

I'm sending this report without having spent a lot of time on it now,
not sure if this ".#" convention comes from outside of emacs.

Thank you!

-- 
Brady

In GNU Emacs 27.0.50 (build 1, x86_64-apple-darwin17.4.0, NS appkit-1561.20 
Version 10.13.3 (Build 17D102))
 of 2018-04-11 built on computer
Repository revision: 57442b6812e9ec565efc39f722e84079dd71d8c0
System Description:  Mac OS X 10.13.3

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Making completion list...

Configured using:
 'configure --disable-dependency-tracking --disable-silent-rules
 --enable-locallisppath=/usr/local/share/emacs/site-lisp
 --infodir=/usr/local/Cellar/emacs/HEAD-57442b6/share/info/emacs
 --prefix=/usr/local/Cellar/emacs/HEAD-57442b6 --without-x --with-xml2
 --with-dbus --with-gnutls --with-imagemagick --with-modules --with-rsvg
 --without-pop --with-ns --disable-ns-self-contained'

Configured features:
RSVG IMAGEMAGICK DBUS NOTIFY ACL GNUTLS LIBXML2 ZLIB TOOLKIT_SCROLL_BARS
NS MODULES THREADS

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny seq byte-opt gv
bytecomp byte-compile cconv dired dired-loaddefs format-spec rfc822 mml
easymenu mml-sec password-cache epa derived epg epg-config gnus-util
rmail rmail-loaddefs mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader cl-loaddefs cl-lib sendmail rfc2047
rfc2045 ietf-drums mm-util mail-prsvr mail-utils term/screen term/xterm
xterm time-date elec-pair tooltip eldoc electric uniquify ediff-hook
vc-hooks lisp-float-type mwheel term/ns-win ns-win ucs-normalize
mule-util term/common-win tool-bar dnd fontset image regexp-opt fringe
tabulated-list replace newcomment text-mode elisp-mode lisp-mode
prog-mode register page menu-bar rfn-eshadow isearch timer select
scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame cl-generic cham georgian utf-8-lang misc-lang
vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms cp51932
hebrew greek romanian slovak czech european ethiopic indian cyrillic
chinese composite charscript charprop case-table epa-hook jka-cmpr-hook
help simple abbrev obarray minibuffer cl-preloaded nadvice loaddefs
button faces cus-face macroexp files text-properties overlay sha1 md5
base64 format env code-pages mule custom widget hashtable-print-readable
backquote dbusbind kqueue cocoa ns multi-tty make-network-process emacs)

Memory information:
((conses 16 208559 10343)
 (symbols 48 20073 1)
 (miscs 40 33 124)
 (strings 32 29281 1750)
 (string-bytes 1 769239)
 (vectors 16 33056)
 (vector-slots 8 675093 10872)
 (floats 8 51 470)
 (intervals 56 232 0)
 (buffers 992 12))