by Daniel SILVA Agence France-Presse BARCELONA, Spain (AFP) — Handset makers are racing to launch their first smartphones with folding screens but analysts warn the technology is still too rudimentary — and expensive — to woo consumers in large numbers for now. Samsung, the world’s biggest seller of smartphones, unveiled a handset that folds open like a book to be a tablet at an event in San Francisco on Wednesday, becoming the first major manufacturer […]