is:issue is:open Hash symbolize_keys stringify_keys does not work on nested hashes

symbolize_keys and stringify_keys does not work on nested hashes:

```
  > {"this"=>{"is"=>:an, "awful"=>:example}, "very"=>:weird}.symbolize_keys
   => {:this=>{"is"=>:an, "awful"=>:example}, :very=>:weird}
```

and:
      > {:this => {:is => :an , :awful => :example}, :very => :weird}.stringify_keys
       => {"this"=>{:is=>:an, :awful=>:example}, "very"=>:weird}
