SAN DIEGO — An F-18 military jet approaching a Marine base crashed near a busy highway in a densely populated San Diego neighborhood Monday, sparking at least one house fire.The pilot ejected, but it wasn't immediately clear whether the pilot or anyone on the ground was injured, officials said.The plane crashed around noon Monday as it prepared to land at Marine Corps Air Station Miramar, said Ian Gregor, a Federal Aviation Administration spokesman. The crash occurred two miles from the base.Gregor did not know the pilot's condition or how many people were in the plane before it crashed near