FOREX-Dollar slips but set to end September with solid gains

* Dollar index could mark best monthly performance in over a year * Markets still keeping an eye on developments in Hong Kong TOKYO/SYDNEY, Sept 30 (Reuters) - The dollar took a breather on Tuesday from its recent rally but was still not far from four-year peak against a basket of major currencies, and could be on track to post its biggest monthly gain in over a year. The dollar index last stood ...