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

This patch adds a command line option (-r/--require) that allows one
to provide modules on the command line that will be 'required' during
node startup. This can be useful for debugging, tracing, memory leak
analysis etc. to be preloaded without explicit changes to the user
script. The option can be repeated to preload multiple modules.

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>
Reviewed-By: Rod Vagg <rod@vagg.org>