"Predicates in Rails rely on standard Ruby semantics for boolean values
and guarantee no singletons whatsoever." - @fxn

This reverts commit 5cad7a0d, reversing
changes made to bb842e8d.

Make it the responsibility of the connection to hold onto an ARel visitor for generating SQL. This improves the code architecture generally, and solves some problems with marshalling. Adapter authors please take note: you now need to define an Adapter.visitor_for method, but it degrades gracefully with a deprecation warning for now.

Addresses an inconsistency in the ActiveRecord::Base.method_missing handling of dynamic finder methods and the passing of the &block parameter for :find_by_attributes.

if a query contains a limit or an offset, ActiveRecord::FinderMethods#find_last had inconsistent behavior.

If the records were loaded, it returned the last record in the cached list.
If they were not, it reversed the order of the query and changed the limit to one.
If the earlier limit was less than the total matching the query in the db,
it would return a different record than if the records had been cached.

This commit changes find_last so that it loads the records when getting the
last record on a query containing a limit or an offset, which makes the behavior consistent.

deprecated the use of the guard_protected_attributes argument with attributes= in AR in favor of assign_attributes(attrs, :without_protection => true)

Signed-off-by: NJosé Valim <jose.valim@gmail.com>

Move JoinDependency and friends from ActiveRecord::Associations::ClassMethods to just ActiveRecord::Associations