[O] Bug: org-toggle-tag always marks buffer modified [9.1.13 (9.1.13-elpaplus @ .emacs.d/elpa/org-plus-contrib-20180618/)]

[Allen Li]

org-toggle-tag always marks the buffer as modified due to how it is
implemented.  It would be better if it did not mark the buffer
modified if it does not change anything.  This is annoying for
org-depend.el (which is contrib, not officially supported) because the
org-blocker-hook set by org-depend.el will mark the buffer modified
whenever an agenda view is built/refreshed.

Glancing at org-toggle-tag, the feature isn't difficult to implement,
but it'll be ugly.

Emacs  : GNU Emacs 26.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version
3.22.24), modified by Debian
Package: Org mode version 9.1.13 (9.1.13-elpaplus @
/usr/local/google/home/ayatane/.emacs.d/elpa/org-plus-contrib-20180618/)