The modest, white-walled Noor Al-Ihsan mosque on the northern outskirts of Phnom Penh was one of the two oldest buildings in the Cambodian capital. When the city, supposedly founded in 1434, celebrated its 550th anniversary in 1984, few if any Phnom Penh buildings predated the nineteenth century. A sign in Arabic and Khmer above the old mosque's entrance dated its foundation to 1813. That was j…