Blender Git Loki

* Curve tilt interpolation types
Just a quickie feature I needed here at work- the previous linear
interpolation of tilt in curves can give nasty pinching problems
when trying to do flowing curves like a ribbon. This commit lets
you choose the interpolation type, between Linear, Cardinal, and
BSpline. The code was already set up for it pretty easily, mainly
needed to make the choice visible to the user.

Example:
http://mke3.net/blender/devel/etc/tilt_interp_types.png

Works on selected curve 'lines', menu in 'curve tools' panel in
edit mode.