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
AS Xml and Json parsers expect the request body to be a real IO object
supporting methods like getc or ungetc which are not specified by the
Rack spec and aren't supported by Passenger or the Rewindable input
wrapper.
We can restore functionality if the AS parsers are rewritten to support
Racks subset of supported IO methods.
