Investors just noticed: Tripadvisor stock is a bargain!Tripadvisor (TRIP 15.08%) stock galloped ahead 18% through 11:05 a.m. ET Thursday after activist investor Starboard Value disclosed that it has taken a 9% stake in the travel advisor. Calling the company "undervalued" (at the time it bought the shares -- we'll have to see if it remains undervalued now that it's up 17%), and "an attractive investment opportunity," Starboard plans to meet with management to discuss ways to improve the stock's price even f ...