fixed problem with RSVP.js using duplicate relative top name

Hi,

I came across a problem with RSVP.js today, when trying to load their amd version with this loader. Apparently, they're duplicating top module name ("rsvp") in the relative dependencies (e.g. "./rsvp/promise"), and loader.js fails to handle that properly. I made a quick fix to get this working, which is in this pull request, but I'm not sure if there's a better way of handling this issue maybe?

Any feedback would be appreciated. Thank you.