src: add -r/--require flags for preloading modules

-r/--require can be used to preload modules on node startup. The option
takes a single module name. The option can be repeated as necessary to
preload multiple modules.

This patch allows 'vendors' (such a cloud host) to inject functionality
that gets executed at application startup without requiring an explicit
require from the user's application. This can be useful to load vendor
specific application monitoring APIs transparently.

PR-URL: https://github.com/iojs/io.js/pull/881


Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: Chris Dickinson <christopher.s.dickinson@gmail.com>