code: function equals(v) {
           return this._x === v.x && this._y === v.y && this._z === (v.z || this._z);
         }
docs: return true if the two vectors are the same
  @name equals
  @memberOf me.ObservableVector3d
  @function
  @param {me.Vector2d|me.Vector3d|me.ObservableVector2d|me.ObservableVector3d} v
  @return {Boolean}