Aug 4 (Reuters) - Britain's FTSE 100 index is seen opening down 2 points at 7473 on Friday, according to financial spreadbetters. * ECONOMY: British shops saw a dip in sales last month, with fashion retailers enduring their worst July for eight years, a survey showed on Friday, adding to evidence consumers are cutting back spending on discretionary items. Britain's economy has slowed as the rise in inflation since last year's Brexit vote and modest pay growth have squeezed consumer