bug#34055: 27.0.50; Documentation of `visited-file-modtime' is inconsistent

[N. Jackson]

In the Elisp manual (info "(elisp)Modification Time") the
documentation of `visited-file-modtime' is inconsistent with its doc
string.

The Elisp manual says

  If the buffer is not visiting a file, this function returns −1.

However, it appears (IIUC) that the function only returns -1 when
the buffer _is_ visiting a file and that file does not exist; the
doc string has it right.

[This was reported in [1] but it remains unfixed in current master.]

[1] https://lists.gnu.org/archive/html/emacs-devel/2018-03/msg00448.html


In GNU Emacs 27.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.22.30)
 of 2019-01-12 built on moondust.localdomain
Repository revision: c48ea7c08c95185ddce266744a1959e0ce6b04e1
Repository branch: master
Windowing system distributor 'Fedora Project', version 11.0.11906000
System Description: Fedora 28 (Workstation Edition)