There was a test that relied on randomness and also checked the result
with very hight precision. That led to a failed test once upon a time.
Now the checking is more benevolent (it should be, as the code is
not expected to be precise) and also the randomness is removed.
SupportSpotsGenerator originally used a heuristic formula. Current
formula is properly derived using known properties of
second moment of area. Several tests of this formula are added.
