Add example failing test for td.explain(object).

[Schoonology]

This is just another random thought, but I found myself instinctively trying the following while test-driving a feature this week:

var bag = td.object(['some_method'])
...
td.explain(bag)

While it was immediately obvious both that we don't support this behaviour now and that what I wanted was td.explain(bag.some_method), it left me wondering how desirable this behaviour would be. I know it would require substantial changes to the way explain and store interact. (If it was easier, this PR would include the working feature!)

[searls]

We've had this issue logged for a long time. #48

I think it's possible without too much rework. We can be a little deft about it if we just slam these objects/constructors into the store with added references of the test doubles that dangle off of them, and then branch accordingly in td.explain.

It'd be hacky to start storing heterogeneous data into the store so it might make sense to instantiate a second store and read from that one when td.explain is a miss on whatever's passed to it.

[searls]

Closing as stale