Code review updates to the bundle manifest.

`__meteor_bootstrap__.bundler` => `__meteor_bootstrap__.bundle`

`bundle.bundle_dir` => `bundle.root`

Rather than placing app_info/appInfo containing the manifest in the
bundle object, instead I'm now placing the manifest directly in the
bundle object.  A) no code currently uses bundle.appInfo.load; B) if
someday we expand the manifest to also include server side resources
than we'd be getting rid of `load` anyway; C) I think it reads better:

`bundle.appInfo.manifest` => `bundle.manifest`

cp_r now returns a list of os-specific relative file system paths as
strings, instead of paths as arrays.

I changed the normalized "path" field in the manifest to be a relative
path instead of an absolute path (`"/static/cat.jpg"` =>
`"static/cat.jpg"`).  This felt better when looking at the manifest; I
think because the path is relative to the bundle root.