When playwright Peter Shaffer's 'Equus' opened on Broadway 35 years ago, it wasn't easy to discern his purpose. Had he set out simply to craft a racketing good script with a philosophical undertow for audience members to puzzle over with their after-theater drinks? Or had he aimed higher? Today 'Equus' feels undated if not yet timeless. And it's as provocative as ever, especially in an energized New Edgecliff Theatre production.