Calling default_scope without a proc will now raise `ArgumentError`.

Deprecated options `delete_sql`, `insert_sql`, `finder_sql` and `counter_sql`
have been deleted.

Removed deprecated methods `partial_updates`, `partial_updates?` and
`partial_updates=`

Method `delete_all` should not be invoking callbacks and this
feature was deprecated in Rails 4.0. This is being removed.
`delete_all` will continue to honor the `:dependent` option. However
if `:dependent` value is `:destroy` then the default deletion
strategy for that collection will be applied.

User can also force a deletion strategy by passing parameter to
`delete_all`. For example you can do `@post.comments.delete_all(:nullify)`

In 94924dc3 the internal default_scope
implementation has changed making it simpler to follow, meaning that the
old usage of with_default_scope has been removed.

With that, order_values was the same argument for both calls to
find_first_with_limit, so remove it and use the existent attribute
for the sake of clarity/simplification.

The previous implementation was necessary in order to support stuff
like:

    class Post < ActiveRecord::Base
      default_scope where(published: true)
      scope :ordered, order("created_at")
    end

If we didn't evaluate the default scope at the last possible moment
before sending the SQL to the database, it would become impossible to
do:

    Post.unscoped.ordered

This is because the default scope would already be bound up in the
"ordered" scope, and therefore wouldn't be removed by the
"Post.unscoped" part.

In 4.0, we have deprecated all "eager" forms of scopes. So now you must
write:

    class Post < ActiveRecord::Base
      default_scope { where(published: true) }
      scope :ordered, -> { order("created_at") }
    end

This prevents the default scope getting bound up inside the "ordered"
scope, which means we can now have a simpler/better/more natural
implementation of default scoping.

A knock on effect is that some things that didn't work properly now do.
For example it was previously impossible to use #except to remove a part
of the default scope, since the default scope was evaluated after the
call to #except.

For example:

    class Post < ActiveRecord::Base
      default_scope -> { where published: true }
    end

    class Comment
      belongs_to :post
    end

When calling `Comment.join(:post)`, we expect to receive only
comments on published posts, since that is the default scope for
posts.

Before this change, the default scope from `Post` was not applied,
so we'd get comments on unpublished posts.

Rails 4.0 has removed attr_protected and attr_accessible feature in favor of Strong Parameters.

These two methods aren't really statistical helper methods and don't
really belong in any other group which is being delegated for querying,
so I'm moving them to their own group of methods.

I've also changed the `:to => :all` hash syntax to `to: :all`.

Right before that in `assert_valid_transaction_action` method we make
sure that `options[:on]` contains values from `ACTIONS` array
(`[:create, :destroy, :update]`) and nothing more (i.e. it could not
contain strings or something else, otherwise the error is raised).

Also I've polished some docs.

Those vars can be used in tasks, which not call load_config.

In commit d1d7c86d I moved setting migrations paths into activerecord's
railtie to remove Rails dependency on databases.rake. However, it
introduced a regression, ENGINE_PATH was not available at the moment, so
engine's migrations where not added properly to paths. Fix was added
at 97a4a771, but it changes a way things work from using ENGINE_PATH to
APP_RAKEFILE. Additionally, the config runs when the code loads, while
previously it ran in the db:load_config rake task

In order to make it more in pair with original version this commit
changes the config to run only on load_config task. This code uses the
fact that defining a task in rake does not overwrite, but only appends.

It also allows to get back to checking for ENGINE_PATH

fixes #10669

While joining_values special treatment is given to string values.
By flattening the array it ensures that string values are detected
as strings and not arrays.

currently `post.comments.find(Comment.first.id)` would load all
comments for the given post to set the inverse association.

This has a huge performance penalty. Because if post has 100k
records and all these 100k records would be loaded in memory
even though the comment id was supplied.

Fix is to use in-memory records only if loaded? is true. Otherwise
load the records using full sql.

Fixes #10509

PostgreSQL escapes single quotes by using an additional single quote.
When Rails queries the column information, PostgreSQL returns the
default values with the escaped single quotes.

#extract_value_from_default now converts these to one single quote each.

Fixes #10881.

This reverts commit 2b817a5e, reversing
changes made to 353a398b.

Conflicts:
	activerecord/CHANGELOG.md

Reason: the build broke

If I have a query that produces sql
`WHERE "users"."name" = 'a         b'` then in the log all the
whitespace is being squeezed. So the sql that is printed in the
log is `WHERE "users"."name" = 'a b'`.

This can be confusing. This commit fixes it by ensuring that
whitespace is not squeezed.

fixes #10982

This lets us do things like call: .find_each.with_index

currently `post.comments.find(Comment.first.id)` would load all
comments for the given post to set the inverse association.

This has a huge performance penalty. Because if post has 100k
records and all these 100k records would be loaded in memory
even though the comment id was supplied.

Fix is to use in-memory records only if loaded? is true. Otherwise
load the records using full sql.

Fixes #10509