add lazy_load_hooks.rb, which allows us to declare code that
should be run at some later time. For instance, this allows
us to defer requiring ActiveRecord::Base at boot time purely
to apply configuration. Instead, we register a hook that should
apply configuration once ActiveRecord::Base is loaded.
With these changes, brings down total boot time of a
new app to 300ms in production and 400ms in dev.
TODO: rename base_hook
* A new module (ActiveSupport::Autoload) is provide that extends
autoloading with new behavior.
* All autoloads in modules that have extended ActiveSupport::Autoload
will be eagerly required in threadsafe environments
* Autoloads can optionally leave off the path if the path is the same
as full_constant_name.underscore
* It is possible to specify that a group of autoloads live under an
additional path. For instance, all of ActionDispatch's middlewares
are ActionDispatch::MiddlewareName, but they live under
"action_dispatch/middlewares/middleware_name"
* It is possible to specify that a group of autoloads are all found
at the same path. For instance, a number of exceptions might all
be declared there.
* One consequence of this is that testing-related constants are not
autoloaded. To get the testing helpers for a given component,
require "component_name/test_case". For instance, "action_controller/test_case".
* test_help.rb, which is automatically required by a Rails application's
test helper, requires the test_case.rb for all active components, so
this change will not be disruptive in existing or new applications.
