bug#31613: 27.0; `with-silent-modifications' in Elisp manual

[Drew Adams <drew.adams@oracle.com>]

1. The Elisp manual mentions this macro only in node `Changing
Properties'.  The macro is not specific to the use case of adding or
removing text properties without marking the buffer as modified.

Seems like it should be described accurately somewhere (else).

2. The English should be corrected.  This text:

"If you wish to add or remove text properties to a buffer..."

should be something like this:

"If you wish to add text properties to a buffer or remove them from a
buffer..."

In GNU Emacs 27.0.50 (build 3, x86_64-w64-mingw32)
 of 2018-03-21
Repository revision: e70d0c9e66d7a8609450b2889869d16aeb0363b5
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --without-dbus --host=x86_64-w64-mingw32
 --without-compress-install -C 'CFLAGS=-O2 -static -g3''