Agence France-Presse: BP’s efforts to place a new containment cap over the gushing Gulf of Mexico oil well could effectively stop the disastrous spill as early as Monday, a US official said Friday. Admiral Thad Allen, who oversees the government’s spill response, said on day 81 of the disaster that an operation to swap in the new cap could begin Saturday and the entire process would take "about three to four days." If successful, the new cap could capture all of the crude spilling into the Gulf and …