new post on resque, retrying, and idempotence

A reaction to [this post](http://eng.joingrouper.com/blog/2014/06/27/too-many-signals-resque-on-heroku/), where they have the same problem as us, but, in my opinion, solved it the wrong way.

This is bit technical but hopefully in the "this team knows its shit" category.
@erinfirst I tried to be vague about our popularity, but the point of "the more popular your business, the more you will run into operational issues" is somewhat important to the point.   Let me know if you see any issues with this.