Fix more small grammar mistakes in the [Getting Started guide](http://edgeguides.rubyonrails.org/getting_started.html#security), in sections 9 and 10. Specifically, within sections 9.1 “Basic Authentication”, 9.2 “Other Security Considerations”, and 10 “What's Next?”. “Rails Guides” is generally capitalized on the site, including on the linked page and in the title of the site, so I capitalized it. “The” is not part of the name of the Ruby on Rails Security Guide – “The” is not in the title on that page. And I added a missing period and a missing colon at the ends of two sentences.
The current approach is broken because it uses a thread local value which means on multi-threaded environments it has to be turned on per thread. Secondly, ActiveSupport::Notifications does not instrument items when there are not subscribers so this flag is unnecessary.
Leave the note for `ActiveModel`, since it can't yet detect mutations (hopefully we can change this in time for 4.2). However, we now detect mutations on all supported types in `ActiveRecord`, so we can note that `_will_change!` is no longer needed there.
Fix bug, when ':dependent => :destroy' violates foreign key constraints Conflicts: activerecord/CHANGELOG.md activerecord/lib/active_record/associations/builder/association.rb activerecord/lib/active_record/associations/builder/has_one.rb
We are moving this behavior out to an object that we would like to keep separated from `ActiveRecord::Base`, which means not passing the class object to it. As such, we need to stop using `instance_exec`, and instead close over the subclass on global type decorators that are applied in `Base`.