Prevent npm preload module to break dev bundles

[m-mujica]

Closes #947

Part of the problem is that the module to preload the npm packages is added at the top of the bundle. So we run into situations like:

{ foo: "/*" };define("foo", function() { var bar = "*/" });

then the amd extension can't see the "define" because the comments regex matches a bunch of the module definition:

The solution I came up with was to push the module with the package.jsons to the bottom of the bundle, that way the first thing the regex matches is the actual AMD modules.

Placing the preloader at the bottom shouldn't matter since it gets executed right away.

[matthewp]

Sounds good to me, nice job.