debugger: repeat last command

Same thing as in the last year: #3921, broken by 9ef9a9dee54

Old regression test is gone, so adding a new one.

Also, error in [helper-debugger-repl.js](https://github.com/joyent/node/blob/master/test/simple/helper-debugger-repl.js#L92), addTest calls quit() function that is out of the scope.