Merge pull request #368 from RobinDaugherty/patch-1

Fix missing `OStream#closed?` method

Author: sealocal

Diff for: lib/iruby/ostream.rb

@@ -11,6 +11,10 @@ def close
       @session = nil
     end
 
+    def closed?
+      @session.nil?
+    end
+
     def flush
     end