[ESS] Symbol's function definition is void: regexp-opt

[Stephen Eglen]

 > 
 >     StEgl> regexp-opt is a function that exists in Gnu Emacs,
 >     StEgl> and seems to be okay too in XEmacs 21.4.13
 > 
 >     StEgl> A similar report for AUC TeX was made last April:
 >     StEgl> http://lists.gnu.org/archive/html/auctex/2005-04/msg00048.html
 > 
 >     StEgl> so the solution seems to be install either the
 >     StEgl> xemacs-base package or the sumo tarball to get the
 >     StEgl> regexp-opt functionality in your xemacs.
 > 
 > Maybe we could improve the error message in the case regexp-opt
 > is not available {for Xemacs}?

we could, but then I wonder where we would draw the line... if other
elements of xemacs-base (or other packages) are missing, we may need
to test for those too.  Maybe a better approach, if possible, would be
to test which XEmacs packages are installed, against a list of what we
require.  But that's a bit of work!

Stephen