Fixed can/util/fixture to be compatible with new StealJS.

With the new StealJS, `steal.config()` throws an error `TypeError: Cannot read property 'length' of undefined`.

Original PR: #1239 

A similar PR by someone else: #1321 

Will dance on a table if this can be merged
I think both, the new and old Steal have a `steal.config` so it will always go in here. I'll probably merge this PR and then also add a test.