Better testing. Fix simultaneous/circular fetch.

Use the osh-iso-test framework for testing with the browser.

Clean up browser chunk-loading scripts along with fixing the
following bugs:

  1. When fetching a module that eventually calls code to
     fetch itself, Dynapack never executes the callback
     in the 2nd (circular) fetch.
  2. For "simultaneous" fetches (for the same module),
     Dynapack never executes the callback in the 2nd fetch.

Add tests for the above fixes.
npm 0.2.4