@scheme*' ->
Also, updates some of the mzlib files to point at `racket/*' libraries rather than to `scheme/*' ones.
- adds a `#:timeout-lock-there' argument to `get-preference' - fixes preference looup in `racket/gui' - make preference names consistently use `GRacket' and consistently fall back on `MrEd' names - fix Emacs-style undo mode while we're at it