Switch to underscore's isEqual for equality tests, use patched difflet.

This moves to use a strict equality check in our deepEqual.  I've also patched difflet to allow for passing in the same deepEqual function (I sent a PR to him https://github.com/substack/difflet/pull/15 as well).  We'll have to fixup the 80 vs "80" type issues in a lot of tests if we land this, since so much fails in existing json files.