The ghost of Raj Rajaratnam still haunts hedge funds. Some make employees sign pledges that they&#39;ve not acted on illicit tips, others snoop on their traders with keystroke-reading software.&nbsp;<br /> <br /> At the compliance meetings everybody has these days, prison isn&#39;t an off-the-wall topic. The illegal-trading probes that netted crooks at more than a dozen funds may have reached an unofficial finale with a whimper last week &mdash; a deal allowing SAC Capital Advisors LLC&#39;s Steven A Cohen to return to th&nbsp;..&nbsp;<br /> &nbsp;