There's no need for a visit to a theme park when you're an investor in the stock market -- at least since this decade began. Over the previous four years, all three major stock indexes have traded off bear and bull markets in successive years. It's been a dizzying ride at times that demonstrates the unpredictability of short-term moves in the stock market. But it's also an excellent reminder that Wall Street is a bona fide wealth-building machine over the long run. Even though the Dow Jones Industrial Avera ...