ISTANBUL — It’s a city so massive that it spans two continents, and even the taxi drivers have to stop and ask for directions. The five daily calls to prayer give Istanbul a conservative soundtrack, while folks who flock to Istiklal Street by the thousands soak up a nightlife that dares even the most adventurous party-goers to keep up. Venders hawk you through the halls of the Grand Bazaar, clamoring for your business in whichever language you’re willing to bargain; still,