(Adds fresh quote, details on auctions, reserves) By Miguel Gutierrez and Michael O'Boyle MEXICO CITY, Feb 17 (Reuters) - Mexico's central bank on Wednesday unexpectedly raised its benchmark interest rate by 50 basis points to 3.75 percent, sparking a rally in the long-battered peso currency, while the government vowed to cut spending. Mexico's central bank also intervened directly in the foreign exchange market to sell dollars as part of a major policy shift to support the peso,