r-maxage is a new directive that takes precendence over s-maxage and max-age. While s-maxage is honored by any shared cache, r-maxage is only taken into account by reverse proxy caches, and thus ignored by proxy and private caches. Setting r-maxage allows applications to ensure the response is only cached by their reverse cache, and thus are able in particular to purge the cache knowing that it will not remain stale in intermediate proxy servers.
By default, this will strip the Set-Cookie response header before storing a cacheable response.
Gemfile.lock was correctly in the .gitignore file, but was also committed to the repository. See http://yehudakatz.com/2010/12/16/clarifying-the-roles-of-the-gemspec-and-gemfile/ Furthermore, it was locked to a version of memcached that I could get to compile on Lion.