handling nicely post processors errors

Added unit tests for 3 postprocessors.
@timlinux, can you please have a look and see if the error layout is ok. (You can trigger an error by running a IF with a female ratio of 1.2
![screenshot from 2014-03-14 13 30 42](https://f.cloud.github.com/assets/233663/2420800/fe5f9c98-ab77-11e3-93af-578e441dff5b.png)