Patch + Test for Lighthouse Issue #2628

Hello,

I've submitted a patch for a bug I came across in ActiveSupport under
Ruby 1.9.1.
https://rails.lighthouseapp.com/projects/8994-ruby-on-rails/tickets/2628

This issue is causing certain requests passing through
ActionController to fail while preparing etags in actionpack-2.3.2/lib/
action_controller/response.rb due to the current implementation of
String.blank?, which tests for blankness using a regular expression.
If content in a database is retrieved by ActiveRecord and interpreted
as valid ASCII-8bit but coerced to UTF-8 during the rendering process
and used for etag generation in ActionController, the body.blank? test
will fail with an unrescuable exception that results in no output
being sent to the user.

I've also included a reduced test case for reproducing the bug, the
original backtrace, and a patch for blank_test.rb demonstrating the
failure under Ruby 1.9.1 and success following the application of the
patch.

This is the first patch I've submitted to Rails core; I'd definitely
appreciate any feedback.

Thanks,

Scott Andreas (@cscotta)
http://sunago.org/