NEW YORK/SAN FRANCISCO, Nov 19 (Reuters) - Investors' reduced appetite for risk is sending a chill through the trading floors of Wall Street and the loft spaces of San Francisco. The large pop in the share price of mobile payments firm Square Inc on its stock market debut on Thursday may not be enough to bring comfort to fellow technology firms such as Dropbox and Cloudera, which are expected to go public in the coming year. The early-morning 64-percent surge in Square's shares came after the firm priced its initial public offering at a 42 percent discount to its last...