Bug 736281 - Implement namespace inheritance.

[Gozala]

I have blogged about namespaces today, where I outlined one annoying limitation that namespaces have in contrast to private names which is this:

let { ns } = require('namespace')
let internals = ns()

let base = {}
internals(base).secret = 'I love JS'

let decedent = Object.create(base)
internals(base).secret // => undefined

With this change last line will return 'I love JS', which I think is more intuitive!

[Gozala]

@ochameau no rush on reviewing this!

[autonome]

why 'frame'? also i'd prefer that the name explicitly indicated it's a namespace.

[Gozala]

@autonome I have decided to wait until we could remove workaround for bug 673468, as most of the code was doing it. Now that this workarounds can be removed (will be done by #429), I think it's ready for another round. Also keep in mind that in the diff you'll see changes from #429 as well since that's where this branches out from (of course you're welcome to review both). You could see only diff for this patch here https://github.com/Gozala/addon-sdk/compare/bug/ns-workarounds@751584...bug/ns-inherit@736281

[autonome]

s/decedents/descendants/ here and elsewhere