Updated comments on Node.cpp
Node fixed errors on set_y_rotation_perpendicular_to_next_bone

Before the method makeRotate from osg was used to calculate the rotation.
But this could lead to wrong rotations since the rotation axis was calculated by them.
Now we force rotation axis to be along bone direction and calculate angle using
dot product.
Node fixed angle errors in set_y_rotation_perpendicular_to_next_bone

Before we always took angle as being positive. Now positive and negative are calculated
and we take the best result.