PARIS, France — Never underestimate the clarity and power of a single idea in our age of chaotic fashions. That's what Jonny Johanson did at Acne Studios. His focus this season? Swedish summer — read rainy and damp — and tents. The brief translated into a compact offer of a-line raincoats, A-line-to-the-knee anoraks and stripy blousons in coated, treated, laminated fabrications, invariably worn with shorts. The result was convincing, not least because it was devoid of the fuss and the bizarre diversions that has given Acne menswear such an odd vibe in the past.