 MADRID Reuters - Thousands of people packed into central Madrid on Saturday to protest against the Socialist government and accuse it of undermining the constitution, in a rally backed by rightist parties. Protesters massed in the Plaza de Cibeles in front of City Hall, waved Spanish flags, called on Prime Minister Pedro Sanchez to resign and shouted out traitor. More than 100 groups - including the conservative opposition Popular Party, centre-right Ciudadanos and the far-right Vox - called... 