JSON Format Post Processor

I'm using the JSON Format Post Processor to make the output of our REST service a little easier to read, but currently when something happens on the server to make it not return valid JSON - exceptions, firewall blocking, etc, the net.sf.json package emits a runtime exception that causes the whole sampler to fail.  Not to be treated as an error (e.g. with a red icon in a result tree listener) but to not appear at all.

This is confusing our testers somewhat so I've updated the class to just log the exception and leave the output untouched and thrown a unit test in too.

I hope you'll consider merging this.