The date range format doesn't accept JS Date() objects.
The date range format doesn't accept JS Date() objects.

These unit tests show the problem. The DateFmt.format and
DateFmt.formatRelative methods do, but DateRngFmt.format
does not. It needs to be more accepting like those other
ones.

iLib-js/iLib,iLib-js/iLib,iLib-js/iLib,iLib-js/iLib,iLib-js/iLib