John Hopewell Chief International CorrespondentBuenos Aires-based Compañía de Cine has swooped on sales rights to “Mostro,” a trenchant take on one consequence of violence in Mexico: Its thousands of women who suddenly join the ranks of Mexico’s “disappeared.”The boutique sales company is introducing the feature to buyers at this week’s Locarno Film Festival where it world premiered Wednesday in the Swiss Fest’s Cineasti del Presente section.The first feature of Mexico’s José Pablo Escamilla,