Fannie Mae saw its share of the government-sponsored enterprise mortgage market shot down again in May, but the company appears to be back on top in June. Freddie Mac reported a healthy $50.03 billion in new business activity during May, beating Fannie Mae’s $45.32 billion for the second month in a row. Freddie’s recent success in the two-horse GSE race has come from its more aggressive purchase of mortgage assets for its investment portfolio: Fannie…