LISBON (Reuters) - Anibal Cavaco Silva, a center-right candidate, won Portugal's presidential election on Sunday in a blow to the ruling Socialist Party already under pressure because of a stagnant economy. Cavaco Silva, a former prime minister vowing to tackle economic woes in western Europe's poorest country, had 50.59 percent of the vote with all but a handful of polling stations reporting, the election commission reported. Leftist maverick Manuel Alegre had 20.72 percent of the vote and 81-year-old Mario Soares, the Socialists' candidate, had 14.34 percent. "I want to be and will be the president of all the Portuguese," Cavaco...