Home prices in California are inexorably closing in on a dubious milestone. With the median price of an existing single-family detached home in the state at $474,370 in August, a 2.6 percent increase from July, a half-million dollar median may be only months away. Two Inland Valley cities already have reached that level. The median in Norco - up 40 percent in the last year - hit $524,750 last month, and Claremont - up 35.9 percent - reached $512,000, in numbers released Friday by the California Association of Realtors and compiled by DataQuick Information Systems. Chino Hills ($487,000), La Verne...