Set @rack_env so custom actions can parse e.g. query string for additional options

[grosser]

No description provided.

[rogercampos]

+1 to this, I've done the same in my fork before realizing on this PL: rogercampos@2955a2e

[tleach]

+1 This would definitely be useful.

For now I'm just overriding the MailView#call method in my Preview class:

  class Preview < MailView
    def call(env)
      @rack_env = env
      super(env)
    end
  end