The holiday season is always kind to Apple, and the last three months of 2015 allowed the company to post a record Q1 profit of $18.4 billion through revenues of $75.9 billion. But given the apparent troubles with demand for its new iPhones, Apple might be at something of a turning point – reflected in a revised Q2 revenue forecast of $50 billion to $53 billion, which is well off the $58 billion it recorded in Q2 2015. For Apple, if it happens, that would be the first year-on-year revenue decline posted in thirteen years, but the company counters that “currency headwinds” have cost it around 15% in earnings over the past 18-months. It says that on “constant currency” measures,…