Add system date check to Fireplace (bug 1044230)

@robhudson this rev (https://github.com/muffinresearch/fireplace/commit/382e7768337f4ca7e0d6a77ce2103a3d163d5134) adds a CasperJS test to your system date branch   https://github.com/mozilla/fireplace/pull/541 that's already pretty much ready to go and was already r+wc.