Tonight is debate night, the single event with the potential to alter the direction of the campaign more than any other. Punters on the PoliticSmarkets website can bet on who will win the debate tonight : the smart money gives Gordon Brown a 10% chance of emerging victorious, David Cameron a 47% chance and makes Nick Clegg the narrow favourite with a 48% probability of winning tonight’s debate.  In one sense Clegg is already the winner just by getting equal billing…