SAN FRANCISCO (Reuters) - Last year, many tech IPOs enjoyed soaring valuations in their Wall Street debut, raining cash on the companies and their investors and boosting concerns about another Silicon Valley bubble. Now, the party is winding down, according to data analyzed by Reuters: Five of the 12 U.S.-based tech companies that went public this year, or 42 percent, priced their shares at a valuation below or nearly the same as their private market value, compared to 24 percent of the 29 th