http://www.myspace.com/unionsquareroundtable" target="_blank">Union Square Round Table Friday, February 29 PA's Lounge, 345 Somerville Ave, Somerville (Union Sq) 9:00 p.m., $8 for 21+ / $11 for 18+ It's the bonus day of the year, so Bonus! is tonight's theme of the (now) bimonthly multi-media performance night that's usually two hour-long segments. How the theme will manifest itself is a surpise until the performance, but frequent musical guest Yoni Gordon usually tries to tie in at least......