Add session.clear for Merb sessions.
Add session.clear for Merb sessions.

janrain/jruby-rack,janrain/jruby-rack,atambo/jruby-rack,jruby/jruby-rack,janrain/jruby-rack,jhstatewide/jruby-rack,atambo/jruby-rack,jruby/jruby-rack,atambo/jruby-rack,janrain/jruby-rack,jruby/jruby-rack,jruby/jruby-rack,jruby/jruby-rack,jhstatewide/jruby-rack,jruby/jruby-rack,jhstatewide/jruby-rack,atambo/jruby-rack,jhstatewide/jruby-rack