Implements streaming CSVs.

Allows unlimited downloads of CSV data using ActiveRecord batch APIs and ActionController response streaming.

Works on Rails 3.2+
Actually pass the options to generate_line.
Make the meat and potatoes of streaming protected.
Add no-cache header to streaming CSV responses.
Disable downstream response buffering of stream
Add header_action method for panels
Use Capybara to better test panel rendering
Add humanize_name option to CSVBuilder#column to control humanization of column name.
Add humanize_name option to CSVBuilder too and pass it to its columns.

This allows a much DRYer code if you have many column namess you don't
want to be humanized. As a bonus, any other transitive option like this
one can be added easily in the future.
Use latest cucumber-rails release
give optional deps in Gemfile their own section
don't specify a version for Devise in the Gemfile
#3005 appears to be resolved!

…though we have to specify a version for sass-rails (#3093)
update sass-rails requirement to work with Rails 3

#3005, #3093
test Ruby 2.1.2
add rspec filter 'focus' and 'skip'
specs for MethodOrProcHelper#render_or_call_method_or_proc_on
Fix for #3155
test fix for #3155
specs for MethodOrProcHelper#render_in_context