/*
 * Draw an Imlib2::Polygon with the specified color
 *
 * Examples:
 *   # create a simple blue right triangle
 *   triangle = Imlib2::Polygon.new [10, 10], [20, 20], [10, 20]
 *   image.draw_polygon triangle, Imlib2::Color::BLUE
 *
 *   # create an open red square polygon
 *   square = Imlib2.Polygon.new [10, 10], [20, 10], [20, 20], [10, 20]
 *   image.draw_poly square, false, Imlib2::Color::RED
 *
 */
static VALUE image_draw_poly(int argc, VALUE *argv, VALUE self) {