[ESS] confusion with Perl and R-mode in XEmacs

[Alex Lancaster]

A user (who is using ESS via XEmacs not GNU Emacs) of the Fedora package
for ESS which I maintain reported that a Perl program (without the ".pl"
extension) would be mis-identified as an R program because of the
following regex in ess-site.el:

(setq interpreter-mode-alist
      (append
       '(("Rscript" . r-mode)
              ("r"       . r-mode)
 )
       interpreter-mode-alist))

Basically this means that XEmacs will see the "r" in "#!/usr/bin/perl"
and open it in R mode.  I can fix in my local package this using a regex
like ".r$" or ".R$", but I would like to get this fixed ultimately in
the upstream package, hence this bug report.

For more details (including a same file that demonstrates the program),
see the downstream Fedora bug:

https://bugzilla.redhat.com/show_bug.cgi?id=631707

Cheers,
Alex