Cycles Hair: Introduction of Cardinal Spline Curve Segments and minor fixes.

The curve segment primitive has been added. This includes an intersection function and changes to the BVH.

A few small errors in the line segment intersection routine are also fixed.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@53825 954f8c5b-7b00-dc11-b283-0030488c597c