"Nurbs birail": an option to use Gordon algorithm

[portnov]

Preflight checklist

Put an x letter in each brackets when you're done this item:

• Code changes complete.
• Code documentation complete.
• Documentation for users complete (or not required, if user never sees these changes).
• Manual testing done.
• Unit-tests implemented.
• Ready for merge.

[portnov]

I tested this again some days ago and have found that:

1. it works
2. but I could not find cases where this gives more precise output than the default algorithm.

So for now I'm closing this. Anyone interested enough can try to merge this locally and try.