If you were superstitious, you might approach the start of the 2012 BBC Promenade Concerts – on Friday 13 July – with a little trepidation.The long-established music bonanza, packing the Royal Albert Hall with “promenaders” every summer, is habitually laden with superlatives, but this time there's more than usual at stake: it now has to live up to the Olympic Games as well. In a recent radio interview, Ruth Mackenzie, director of the London 2012 Festival, declared that this year's Proms – a major component of the festival – can be called “a once-in-a-lifetime experience”. Oh yes? Is that so?