Signed-off-by: NJeremy Kemper <jeremy@bitsweat.net>

let the rails command recurse upwards looking for script/rails, and exec ruby on it for better portability [Xavier Noria] (Closes #4008)

Signed-off-by: NJeremy Kemper <jeremy@bitsweat.net>

Signed-off-by: NJeremy Kemper <jeremy@bitsweat.net>

This reverts commit eec2d301.

This commit broke tests. You cannot have a file called "bundler" on the load path.

  * Add the Rack::Sendfile middleware
  * Make the header to use configurable via config.action_dispatch.x_sendfile_header (default to "X-Sendfile"). 
  * Add Railties tests to confirm that these work
  * Remove the :stream, :buffer_size, and :x_senfile default options to send_file
  * Change the log subscriber to always say "Sent file"
  * Add deprecation warnings for options that are now no-ops

Note that servers can configure this by setting X-Sendfile-Type. Hosting companies and those creating packages of servers specially designed for Rails applications are encouraged to specify this header so that this can work transparently.