By JEFFREY GETTLEMAN MOGADISHU, Somalia — In the end, it all came down to a single forgotten bolt. Marc Aubrière, a French security adviser who was held hostage in Somalia for more than a month, said he simply slipped open a lock on the inside of his cell door — a lock his captors had somehow overlooked. He then tiptoed past the sleeping guards, who are part of an extremist Islamist group that...