repl: To exit, press ^C again or type .exit.

When the user hits `^C` in the REPL show more info about `.exit`.

The idea was to give more info to the user when they hit ^C.
Current version just displays `(^C again to quit)` and most
of the users are not aware of the `.exit` command that would
Exit the repl.

PR-URL: https://github.com/nodejs/node/pull/3368


Reviewed-By: James M Snell <jasnell@gmail.com>