In fact fixed in easiest way -- always re-calculate knots array
on topology changes.
After some discussion with Ton we agreed on that having manually
editable knots is not intuitive and user should only define
cyclic/endpoints flags and knots would be re-calculated based
on this flags.
This means that it's unnecessary to have special logic for knots
manipulating in some topology changing tools and they could just
re-calculate knots for the whole nurb, without worrying that knots
could have been manually edited.
7ed68ac4ef