Bump Rails to 3.2.18, to get the latest security updates
Merge pull request #293 from alphagov/bump_rails_to_3.2.18

Bump Rails to 3.2.18, to get the latest security updates
Add a global_type column to the sites table

- Due to doing this, make global_http_status and global_type stay in
  sync with each other by setting both attributes in previous data, with
  some manual SQL in a migration. Following @jennyd's lead with what she
  did with mappings.
- This will eventually replace global_http_status, in the unresolved
  mappings process.