Economist: SIEBEN LINDEN, a hamlet in former East Germany, half-way between Hamburg and Berlin, looks deceptively normal. There is a cluster of houses, some fields, a few cars parked by the side of the road and a small shop, all set against the backdrop of a looming pine forest. Closer inspection, however, reveals a few peculiarities. Several of the modern-looking buildings turn out to be made of wood, straw and mud. There are huge quantities of logs, because wood-fired stoves and boilers …