Fixed vertical alignment of homepage promo slots

From <img src="http://f.cl.ly/items/390t412P1R1d0J0a1X3K/Screen%20Shot%202013-02-14%20at%2010.57.56.png"> to <img src="http://f.cl.ly/items/1S0300220q351c0d3o1s/Screen%20Shot%202013-02-14%20at%2011.00.25.png">