Edit Curves support

[Dan Masquelier]

For NurbsPath:

For a NurbsPath, when context.mode is 'EDIT_CURVE', and you have a curve spline point selected (equivalent of a mesh vertex), the following will work for selecting points on the spline.

obj = bpy.context.active_object
current_spline_index = 0
current_point_index = 0
obj.data.splines[current_spline_index].points[current_point_index].select = True

Need to make equivalents of select_next_vertex and select_prev_vertex for curves, so select_next_spline_point select_prev_spline_point`.