Here's a fix for probuilder's spline twisting problem

I don't think this ever got fixed, but there's a post on it at the old forums: http://www.procore3d.com/forum/topic/2252-probuilder-splines/

I implemented a fix that seems to do the trick along the lines suggested in that post. Here's my Spline.cs

Before:



After:



It would be nice to get this fix into the actual package so I don't have to worry about updates stomping my fix.