rails/rails — pull request #8812 by rubys (2013-01-08 12:27:20+00:00)
Title: Eliminate Rack::File headers deprecation warning

See http://intertwingly.net/projects/AWDwR4/checkdepot/section-6.1.html
rake test produces:
"Rack::File headers parameter replaces cache_control after Rack 1.5."

Despite what the message says, it appears that the hearders parameter change
will be effective as of Rack 1.5:

https://github.com/rack/rack/blob/rack-1.4/lib/rack/file.rb#L24
https://github.com/rack/rack/blob/master/lib/rack/file.rb#L24