Update to experimental r13565

LPE Powerstroke: add Centripetal Catmull-Rom interpolator

properly attribute code

To help the SVG WG discussion on powerstroke, a quick code-up of centripetal Catmull-Rom interpolation. The code probably needs a clean up pass, and more generally, the interpolation functions should move into 2geom or at least into a .cpp file. - Add Catmull-Rom interpolation to powerstroke interpolation options - Add LPE Interpolate points

Experimental merge of Ponyscape features into trunk (will not compile)

cleanup spiro code

more spiro cleanup

Powerstroke: add smoothness parameter for CubicBezierJohan

split interpolator code from main powerstroke code