Six months ago, SL Green Realty’s CEO Marc Holliday spoke of a “dark cloud” hanging over Manhattan’s commercial real estate market. Since then the weather appears to have cleared up considerably. The office REIT more than doubled its funds from operations (a measure of cash flow) year-over-year in the second quarter to $357.8 million on the back of stronger-than-expected leasing velocity, the company said in an earnings call Thursday.