Make test.sh exit with nonzero status if tests fail
This behavior makes "make verify" actually fail when the tests fail,
which is what it's supposed to do.
Add options to test-ratelim.c to check its results
The new options let you specify a maximum deviation of bandwidth used
from expected bandwidth used, and make test-ratelim.c exit with a
nonzero status when those deviations are violated.
This patch also adds a test-ratelim.sh script to run test-ratelim with
a few sensible options for testing.
