jsDump: Add a depth parameter to object parsing

In projects with deep object graphs, like Ember, walking all properties of an an object recursively can end up walking most of memory. This causes the browser to run out of memory and kill the tab/thread.

This introduces a depth option for the parse function, which is used in places where an strictly accurate output of an object is not needed, for instance, when showing two un-equal objects in test output.

I've hard-coded the depth to 5 for output value comparisons. I think this should possibly be configurable? However I'm unsure where/how to reference that. I thought I could read a value right off `config.currentModuleTestEnvironment`?

This is the product of a long afternoon of debugging, and I'm happy to do whatever I must to save others form being bit by the same issue.
I'm not sure where you got that idea from. `QUnit.equiv` doesn't depend in any way on `QUnit.dump`.

Even if it's necessary to set `maxDepth` here and resetting it afterwards, of which I'm still not convinced, the value has to be configurable. An inline value can only be changed by editing the QUnit source file.