As the global war on terror approaches the start of its eighth year, the NYPD says it has never been more prepared - but also warns that the city can never let its guard down. In a two-part series, Daily News reporter Patrice O'Shaughnessy looks at the terror threat in New York - and around the world. Sunday's installment focuses on an NYPD undercover officer who dug deep into the potential terrorists in our midst. A young undercover city detective spent four years in the shadowy world of terrorist wanna-bes - taking part in jihadist discussions and training in parks...