Checks orientation of the surface. 

true if "natural" and "nominal" normals are opposite (surface is "left-handed"), false - otherwise (surface is "right-handed").

Let U and V be surface's partial derivatives by U and V respectively (at some point). Consider two normals:

• "natural" normal is computed as [U x V] (i.e. cross product of partial derivatives).
• "nominal" normal is the vector returned by evalPoint method.