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 kept it light, but with a footnote to a more detailed explanation.  LMK what you think