Fix for #102. The mirror is now called "shared" and is only ever called once per startup. Jasmine and mocha-web can both use this shared mirror for now. Ideally, each framework should request its own mirror, but I tried that and it was clunky so it needs some more thought!
Merge pull request #112 from meteor-velocity/bug/102

Fix for #102 - Mirror: exited with code 254 signal null