I'm migrating a Ruby on Rails application from 3.0 to 3.1 and ran into some problems with the change of the JSON backend.

The line `ActiveSupport::JSON.decode(some_variable)` gives me the MultiJson::DecodeError `nesting of 20 is too deep`.
The variable I'm trying to decode is indeed heavily nested (max 29 levels).

The maximum nesting level should be changeable with the `:max_nesting` option (['Nesting too deep' error while retrieving JSON using HTTParty](https://stackoverflow.com/questions/9917666/nesting-too-deep-error-while-retrieving-json-using-httparty)) but this doesn't seem to work.

Both `ActiveSupport::JSON.decode(some_variable, :max_nesting => false)` and `ActiveSupport::JSON.decode(some_variable, :max_nesting => 100)` result in the same error.

Is there a way to pass the `max_nesting` option or set it application wide?