Mongo Shell should support concept of module loading.

While load() is fine for loading and executing an external javascript script, if we're going to move the shell towards being a more general purpose testing and scripting environment, it's going to need a system for loading modules that can track what modules are already loaded, and avoid reloading them, and a convention for avoiding polluting the global namespace.

I'm familiar with the module system from Dojo (dojotoolkit.org). The commonjs initiative (commonjs.org) also has a specification for module loading, for which implementations may be available.