[ESS] feature request: look more places for R on windows

[Ross Boylan]

I've installed R as a regular user on Windows 7.  I accepted the default 
path of
C:\Users\rdboylan\Documents\R\R-2.15.3\
Apparently ESS doesn't look there, because it says it couldn't find an 
installed version of R when it starts.  It would be nice if it checked 
for regular user installations too.

This is not a big deal for me since I have (setq inferior-R-program-name 
"C:/Users/rdboylan/Documents/R/R-2.15.3/bin/i386/Rterm.exe") in my 
.emacs file.  So M-x R works fine.  But my solution is quite brittle, 
because I have to remember to update it when I change my R version.

Of course, I welcome suggestions for better approaches I could 
implement.  I suppose I could find the code that currently searches for 
R versions and adapt it to work for my directory.

Thanks.
Ross Boylan