Add casper test for #541 

This is derived from the casperJS branch so there's a bunch of commits from that. :bomb:

@robhudson this rev adds a CasperJS test to your ystem date branch https://github.com/muffinresearch/fireplace/commit/5bac6b546329270e6cc229141a2f5c3868b7686c Once the casper tests branch lands (See #556) you could just crib the test and re-open https://github.com/mozilla/fireplace/pull/541 that's already pretty much ready to go.