In another manifestation of what Wall Street refers to as “headline risk,” the enormous investment portfolios of Fannie Mae and Freddie Mac have re-entered the crosshairs of GSE reformers. Outgoing Federal Reserve Chairman Alan Greenspan, in what is likely his final official jab at the behemoth government-sponsored enterprises, has reaffirmed his strong support for the Senate’s GSE reform legislation. In a letter sent earlier this month to three members of the Senate Banking, Housing, and…