In the new issue of Philadelphia Weekly: Steve Lehman Trio Sun., Apr. 15, 8pm. Free. The Rotunda, 4014 Walnut St. 215.573.3234 www.arsnovaworkshop.org Steve Lehman came to town last year and performed his “Nos Revi Nella” for alto sax and string quartet. That’s backwards for Allen Iverson — a man Lehman sees not just as a point guard but a great