Requirejs test

I wrote a regression test for the bug @alicoding hit when Filer and Buffer weren't usable via require.js.

The tricky bit about testing this is that I have to isolate this test from our other tests, since you can't cleanly mix requirejs and browserify build steps.  My solution is to run two separate mocha commands for each set of tests.  I also need to modify the GLOBAL to shim XHR in this test, so another reason to isolate things.