Bug 1056214 - Use the addon-sdk repo's JSM modules when -o is used

I don't really like `modules/system` layout in `lib` as I find naming confusing from the add-on SDK perspective. How about a `source/lib/jsm/Startup.jsm` or `source/lib/shared/Startup.jsm` ? I would also expect these to be added to an repo since sdk modules are going to load them.