Add browserifytest to Cakefile

This adds the failing browserify test @pwnall requested. How it works:

1. Run `cake browserifytest` on this branch. The test passes!
2. Run `git revert c2b797baaa65280d2a59c7086b339f63a9cc842d` (c2b797baaa65280d2a59c7086b339f63a9cc842d fixed browserify support.)
3. Run `cake browserifytest` again. The test fails!