Fix that #pluck wasn't rescuing ThrowResult, meaning it would blow up when failing to construct_limited_ids_condition.
Add coverage for the fact that pluck without an argument returns all the table's columns.
No point in memoizing a simple literal string.
Make NullRelation a bit more like a real relation by returning 0 for #calculate(:count)
Rather than raising ThrowResult when construct_limited_ids_conditions comes up empty, set the relation to NullRelation and rely on its results.

This will help avoid errors like 2fcafee250ee2, because in most cases NullRelation will do the right thing. Minor bonus is avoiding the use of exceptions for flow control.
Add note about upgrading custom routes from `put` to `patch`.
Prevent side effects in `Hash#with_indifferent_access`.
rewrites AR's reload documentation

* It is no longer true that options are passed to find.

* Documents that ActiveRecord::RecordNotFound may be raised.

* Documents that the reload happens in-place.

* Documents that caches are wiped.

* Documents that the method returns self.

* Documents a couple of use cases.
Fixing a failing railtie test by using the ENV variable to specify a
particular controller to search for in rake routes.
revises the documentation of ActiveRecord::Relation#find_or_create_by [ci skip]

* Inspect uses double quotes.

* Inspect puts a hash as in #<User ...>.

* Documents the return value, and makes explicit it can be an invalid record.

* Documents the method is not atomic.

* Documents a way to handle UNIQUE contraint violations in the event of a race condition.

* Removes the "Examples" header according to our guidelines.
Remove active_support/json/variable was deprecated.
Remove ActiveSupport::Benchmarkable#silence was deprecated.
Remove active_support/testing/pending.rb was deprecated.
Remove :confirm and :disable_with options for ActionView::Helpers::UrlHelper#link_to and #button_to were deprecated.
Remove link_to_function / button_to_function from ActionView::Helpers::JavascriptHelper were deprecated.
Remove :confirm and :disable_with options from ActionView::Helpers::FormTagHelper were deprecated.
Remove action_controller/vendor/html-scanner.rb was deprecated.
Remove ActionController::RecordIdentifier was deprecated.
Remove #sum with a block was deprecated.
Remove ActionView::Template#mime_type was deprecated.