Most apps upgrading from 3.x will have options for mass assigment in
their application.rb and environments/*.rb config files. Rather than
just raising a NoMethodError when copying the config, this commit
adds a warning message until either the protected_attributes gem
is installed or the relevant config options are removed.

In the end I think the pain of implementing this seamlessly was not
worth the gain provided.

The intention was that it would allow plain ruby objects that might not
live in your main application to be subclassed and have persistence
mixed in. But I've decided that the benefit of doing that is not worth
the amount of complexity that the implementation introduced.

The new option allows any Ruby namespace to be registered and set
up for eager load. We are effectively exposing the structure existing
in Rails since v3.0 for all developers in order to make their applications
thread-safe and CoW friendly.

Get rid of ActiveModel::Configuration, make better use of
ActiveSupport::Concern + class_attribute, etc.

can be configured by setting config.active_record.migration. Setting to :page_load will raise an error on each page refresh if there are migrations that are pending. Setting to :page_load is defaulted in development for new applications. 

Active Record should be lazy loaded and this pull request
forced Active Record to always be loaded after initialization.

This reverts commit 8cd14c0b, reversing
changes made to 2f0c8c52.

minor

Clean up the cache before the request in case we are running in the reload_classes_only_on_change schema.

This can be turned off by setting `config.reload_classes_only_on_change` to false.

Extensions like Active Record should add their respective files like db/schema.rb and db/structure.sql to `config.watchable_files` if they want their changes to affect classes reloading.

Thanks to https://github.com/paneq/active_reload and Pastorino for the inspiration. <3

Move sandbox to AR and pass the sandbox as a value. This way, other ORMs like Datamapper can also have their own sandboxing in rails console.

added config.active_record.whitelist_attributes which creates an empty whitelist of attributes available for mass assignment for all models in your app

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

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