Allow running r.js in either Node or Java

[jmbowman]

I added a configuration option and some minor code changes to allow using Node instead of Java to run the optimizer. In my use case making this switch reduces the duration of the run by a factor of 4. It means using UglifyJS instead of Closure Compiler, but in my case the size difference between the output of the two is negligible.

[etianen]

Haha! I was going to add this myself, but you beat me to it! I've got a project that uses a loader plugin I wrote to inline base64 representations of images, and on my quad-core laptop the compilation step takes around 5 minutes! This will be a welcome addition.

The only thing I'd ask, would be if you could change the setting from REQUIRE_NODE to REQUIRE_ENVIRONMENT, which can be "node" or "rhino", defaulting to "rhino". That would match the equivalent settings used internally by NodeJS.

Also, a line in the README describing he setting would be good.

Thanks for your input! :D

[jmbowman]

Anything in particular still holding back the merge, or just haven't had time to work on django-require recently?

[etianen]

Nothing at all (other than GitHub never told me you'd made those changes 13 days ago).

Thanks!

[etianen]

So, I'd love to hear your opinions on issues #6 and #7, particularly #7