By Svea Herbst-Bayliss BOSTON (Reuters) – Hedge fund billionaire William Ackman is facing mounting pressure as his high-stakes bet against nutrition and weight loss company Herbalife enters its second year, but for now, his investors look ready to stick with him. The founder of Pershing Square Capital Management has seen the value of his $1 billion short play against Herbalife lose nearly three-quarters of a billion dollars in 2013, making it one of the 10-year old fund’s riskiest bets. …