These tests are quite dependent on the exact form
of the default RACE_GROUP macros:

1.  They use Thread as the thread number.
2.  They expect to be able to change it during a function.
3.  They expect that that change will make it seem as if the old
	thread is still in the function after the routine, so that a
	call with the new thread will find a race.
4.  expect_zeroness knows that all threads are stored in a single long.
