Avoid db connection on application boot

[jswanner]

awesome_nested_set can prevent rake assets:precompile from successfully running. In what seems like a esoteric condition -- a database not existing and a class using awesome_nested_set being loaded on application boot -- is a very real possibility now on heroku combined with Rails 3.1's rake assets:precompile, especially if you are using something like Refinery CMS, or a Rails engine that you do not control the code.

To reproduce:

A model (could be from an engine or something):

class Category < ActiveRecord::Base
  acts_as_nested_set
end

And in config/application.rb:

config.to_prepare do
  Category.class_eval do
    def to_s
      title
    end
  end
end

Then run RAILS_ENV=env_with_no_db rake assets:precompile -- or deploy to heroku -- and you will see assets are not being precompiled.