The sheriffs have come to town for hedge-fund managers. A federal roundup Wednesday included the arrest of four people and the unsealing of charges against three others. The FBI, which has been casting an increasingly wider net for miscreant money managers, arrested Todd Newman, who headed technology trading for Diamondback Capital Management, in Boston; Jon Horvath of Sigma Capital Management in Manhattan; and Danny Kuo, a Whittier Trust Co. fund manager, in California. Anthony Chiasson, who cofounded Level Global Investors hedge fund, turned himself in to agents in New York. Charges were also unsealed against three other hedge-fund employees, including two who are reportedly cooperating with investigators.