Use path join to construct the path instead of concatenating strings.
Replace backslash with double backslash so that they are escaped
correctly in the string passed to REPL.
PR-URL: https://github.com/nodejs/node/pull/3608
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>