Now that subtests in TAP are supported again, I want to correct the
great historical injustice of 7912f9b7dc9e2d3f6cd81892ef6aa797578e9f06
and put those subtests back.
Much more work like this is possible, of course. I just wanted to get
this out of the way since the code was already written and I've had this
on my list for, uh, 7 years.
