When the Mojito first swept U.S. bars and restaurants a few years ago, that rum-mint-and-lime tropical cocktail encouraged bartenders who longed to serve drinks by muddling the ingredients, smashing them in the bottom of the mixing glass with sugar and spirit. Soon, the muddler went from curiosity to an essential tool behind any cutting edge bar. It also meant that another lime based drink from south of the border, the Caipirinha (made from the Brazilian rum-like spirit cacha