After much thought, I've decided that `Restart' on r is not a

particularly useful keypress, particularly given how easy it is to
confuse it with `Redo'. So both r and ^R are now Redo, and Restart
is relegated to being a menu-only option.

git-svn-id: svn://svn.tartarus.org/sgt/puzzles@5796 cda61777-01e9-0310-a592-d414129be87e