Does anyone know what is causing auto-generated config.rb file for stylesheets?

Recently a particular Rails app I’m working with began to auto-generate
a
file app/assets/stylesheets/config.rb. It looks similar to a Compass
configuration file, but this app does not use Compass.

I’ve found a couple threads about this, but so far no answers.
http://stackoverflow.com/questions/15003841/rails-assets-stylesheets-config-rb
https://github.com/rails/sass-rails/issues/141

Some relevant info about the app’s gems:
rails (3.2.12)
sass (3.2.6)
sass-rails (3.2.5)
sprockets (2.2.2)

Most of all I want to know why the file is now appearing and why it is
important. Should I just git-ignore it? Is it best to add the file to
version control?