Readd use of TAP subtests

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.