CRBSPC ( dim, order, nctrl, ctrl, knots, nprops, props, bc, ifail )
===================================================================

  Create B-curve from B-spline data

Receives:
  KI_int_dimension         *dim            --- dimension of control points
  KI_int_order             *order          --- order of curve
  KI_int_nitems            *nctrl          --- number of control points
  KI_dbl_coefficients       ctrl[dim*nctrl] --- control points
  KI_dbl_knots              knots[]        --- knot vector
 <KI_int_nitems>           *nprops         --- number of curve properties
  KI_cod_papr               props[nprops]  --- array of curve properties

Returns:
  KI_tag_b_curve           *bc             --- B-curve
  KI_cod_error             *ifail          --- failure indicator

Specific errors:
  KI_bad_knots              invalid knot vector
  KI_weight_le_0            weights are non positive
  KI_insufficient_points    insufficient control points
  KI_bad_parametric_prop    property not applicable

Description:
  This function creates a B-curve from B-spline data - i.e. a set
  of B-spline vertices (control points), and a knot vector. The curve may be
  either periodic or non-periodic, and the 'props' array supplies this
  information.

  Dimension of control points 'dim':
  . For rational curves 'dim'=4.
  . For non-rational curves 'dim'=3.

  Order of the curve 'order':
  . The order of the curve = degree + 1.
  . The minimum order is 2.

  Number of control points 'nctrl':
  . For non-periodic curves 'nctrl' >= 'order'.
  . For periodic curves 'nctrl' >= 3.

  Control points 'ctrl':
  . For non-rational curves, the control points are points in 3-space and
    must be supplied [x0,y0,z0,x1,y1,z1,...].
  . For rational curves each vector contains a point in 3-space followed by a
    weight for the point. The points are supplied [x0,y0,z0,w0,x1,y1,z1,w1,...].
    The weight must be positive. Increasing the weight of a control point will
    pull the curve closer to that point.

  Knot vector 'knots':
  . The knot values must form a non-decreasing sequence.
  . For non-periodic curves there must be ('nctrl' + 'order') knot values,
    the maximum multiplicity of an internal knot value is ('order' - 1), and
    the maximum multiplicity of an end knot value is 'order'.
  . For periodic curves there must be ('nctrl' + 1) knot values, and the
    maximum multiplicity of any knot value is ('order' - 1).  If the periodic
    knot has multiplicity greater than 1, repetitions must be given at the end
    of the knot vector.

  Number of properties 'nprops':
  . Gives the number of properties in the 'props' array.
  . There is only one property (periodicity) and so 'nprops' must be either 0
    or 1.

  Properties array 'props':
  . PAPRPE - the curve is periodic (default is non-periodic).