function isFullCircle(aBnds) {
    return Math.abs(aBnds[1] - aBnds[0]) > twoPI - 1e-14;
}
is sector a full circle?
... this comes up a lot in SVG path-drawing routines

N.B. we consider all sectors that span more that 2pi 'full' circles

@param {2-item array} aBnds : angular bounds in *radians*
@return {boolean}