Adjust the README instructions to have --interactive in the R
startup invocation, so base graphics display automatically.

Easy, peasy.  The only trick here is to use parse() in the case that
compile-file-for-emacs is not being asked to load the `compiled' file.

It was surprisingly hard to intuit getwd() and setwd(), what with
apropos("dir") and apropos("cwd") failing.  Nevertheless, they exist
and function, so use them for the interface (but not slimefun)
functions.

Link to them from README for webby goodness.  (Actually for webby
goodness I have to call them BUGS.org and TODO.org, *sigh*).