PARIS (AP).- The Louvre Museum and the royal palace at Versailles were closed Thursday because of a French museum workers’ strike that appears to be gathering steam. Frustrated tourists gathered outside the landmark pyramid in the courtyard of the Louvre, blocked off by workers. They are protesting government plans not to replace half of retiring public servants, which will affect the country’s national museums. The strike began at the Pompidou Center for modern art last month and workers at other national museums joined in Wednesday. Union leaders met with Culture Minister Frederic Mitterrand on Wednesday afternoon but won no concessions, and unions said the strike gained