Looking in :Stencyl\plaf\haxe\lib\openfl\1,1,1\flash\display\Graphics.hx you will see the following:
/**
* Draws a curve using the current line style from the current drawing
* position to(anchorX, anchorY) and using the control point that
* (<code>controlX</code>, <code>controlY</code>) specifies. The current
* drawing position is then set to(<code>anchorX</code>,
* <code>anchorY</code>). If the movie clip in which you are drawing contains
* content created with the Flash drawing tools, calls to the
* <code>curveTo()</code> method are drawn underneath this content. If you
* call the <code>curveTo()</code> method before any calls to the
* <code>moveTo()</code> method, the default of the current drawing position
* is(0, 0). If any of the parameters are missing, this method fails and the
* current drawing position is not changed.
*
* <p>The curve drawn is a quadratic Bezier curve. Quadratic Bezier curves
* consist of two anchor points and one control point. The curve interpolates
* the two anchor points and curves toward the control point. </p>
*
* @param controlX A number that specifies the horizontal position of the
* control point relative to the registration point of the
* parent display object.
* @param controlY A number that specifies the vertical position of the
* control point relative to the registration point of the
* parent display object.
* @param anchorX A number that specifies the horizontal position of the
* next anchor point relative to the registration point of
* the parent display object.
* @param anchorY A number that specifies the vertical position of the next
* anchor point relative to the registration point of the
* parent display object.
*/
function curveTo(controlX : Float, controlY : Float, anchorX : Float, anchorY : Float) : Void;
Maybe that works?