Merge pull request #93 from jrochkind/workaround_mri_at_exit_bug

workaround MRI bug in preserving exit status in at_exit

lib/celluloid.rb

@@ -73,7 +73,17 @@ def shutdown
   end
 
   # Terminate all actors at exit
-  at_exit { shutdown }
+  at_exit do
+    if defined?(RUBY_ENGINE) && RUBY_ENGINE == "ruby" && RUBY_VERSION >= "1.9"
+      # workaround for MRI bug losing exit status in at_exit block
+      # http://bugs.ruby-lang.org/issues/5218
+      exit_status = $!.status if $!.is_a?(SystemExit)
+      shutdown
+      exit exit_status if exit_status
+    else
+      shutdown
+    end
+  end
 
   # Class methods added to classes which include Celluloid
   module ClassMethods