fix in damping coefficient calculation
previously not correct. Since auto_damping_ratio > 1 (implicityly == 2),  damping_factors.back() * (1 - this->auto_damping_ratio) does not make sense.
Using this calculations, real damping factors were as follows: 1, -1/2, 1/8, ....
Merge pull request #109 from ppkk/devel

fix in damping coefficient calculation. Not sure about that, please look at it carefully. This is potential source of errors difficult to find. But I thing, that it was really wrong up to now.