Ruby 1.9 compat: define __setobj__ for Delegator

activesupport/lib/active_support/deprecation.rb

@@ -178,15 +178,19 @@ def warn(callstack, called, args)
 
     class DeprecatedInstanceVariable < Delegator #:nodoc:
       def initialize(value, method)
-        super(value)
         @method = method
-        @value = value
+        super(value)
+        __setobj__(value)
       end
 
       def __getobj__
         ActiveSupport::Deprecation.warn("Instance variable @#{@method} is deprecated! Call instance method #{@method} instead.")
         @value
       end
+
+      def __setobj__(value)
+        @value = value
+      end
     end
 
   end