Rails 3.2.6 session[:_csrf_token] different from meta tag
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I have a Rails application that I've upgraded from 3.0.7 to 3.2.6. I use Dalli and memcached for my session store.

Since I've upgraded, I've started getting `WARNING: Can't verify CSRF token authenticity` errors, and my sessions are being reset.

I call `csrf_meta_tags` in my header.

In my ApplicationController, I've overridden `verify_authenticity_token` in order to check out what the app thinks the csrf_token is.

    def verify_authenticity_token
      verified_request?
      Rails.logger.info "+++ VERIFY AUTH TOKEN +++"
      Rails.logger.info session.inspect
    end

I submitted a form from my app, and the session data written to the logger was:
`{"_csrf_token"=>"4OQ47F2py+l12lLSTnq0RTmyPbmPi2UGMZaPhMG6vVQ="}`

This differs from the value set on the page in the meta tag and from the value submitted with the form:
`{"authenticity_token"=>"qMsdBkTHoBH09+X0tnyoPsbtc752yKjCVHddrcufd7g="}`
