[ESS] R transcript file name suffix

[William McCoy]

I have been using ESS mainly for R for over 20 years.  I use R less 
frequently in recent years and I have not tried to use transcript mode 
for a while.  I have always used .Rt as the suffix for my R transcript 
files.  I have hundreds of them and I have retained the following line 
in my init.el:

(setq auto-mode-alist (append '(("\\.[Rr]t\\'" . R-transcript-mode))
       auto-mode-alist))

That line no longer has any effect on ESS and my .Rt suffix no longer 
works; ESS expects .Rout as the suffix.

How can I customize my ESS version 18.10.3snapshot to use .Rt as my 
transcript file name suffix?

Thanks,
Bill