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.
Ah, I'm using British Music Press Subject/Verb Agreement™.  Since I'm not British, nor in the music press, will change to _is_.