Fix #381 - provide way to trigger clean shutdown from command line.

[humphd]

I've used a slightly modified version of what Brian suggested, and it does basically what I wanted. In the process I found that we can't rely on node-redis' quit command to fire its callback all the time.

[alicoding]

r+

[humphd]

@alicoding when you have time, do you want to do an npm bump for this?

[alicoding]

done