Check that there are adequate tests for recursive slices.

[jmalloc]

In reviewing PR #27, which moves the recursion detection logic, I noticed this paragraph in the documentation of reflect.Type.Pointer():

If v's Kind is Slice, the returned pointer is to the first element of the slice. If the slice is nil the returned value is 0. If the slice is empty but non-nil the return value is non-zero.

I'm not sure about that "first element of the slice" thing, it seems like that might incorrectly render the recursion markers at the elements of the slice, rather than at the slice itself. We probably just want to make sure there is a test for this case.