The longstanding sibling rivalry between the two biggest members of the United Arab Emirates, always complex, has taken a remarkable turn.  For years, as its neighbor on the Persian Gulf, Dubai, engaged in a frenzy of construction and deal-making, Abu Dhabi -- the capital of the UAE and owner of its deepest petroleum reserves -- was mostly content to keep its ambition in check. Its caution underscored old stereotypes about its role as the wary, wealthy older brother...more