Fourth-quarter results have been mixed so far for makers of heavy-duty mining and construction equipment. Investors don't seem to mind. Caterpillar (CAT) earnings slipped 37% and sales dipped 7%, as both missed expectations. Crane maker Manitowoc (MTW) posted gains that comfortably topped Q4 sales and earnings estimates. But the seven equipment makers that make up the industry group rose last week, and the group rose to a No. 14 ranking in