Yet more work on the internal link detection logic in Stencil.
Yet more work on the internal link detection logic in Stencil.

Now an internal link is a link on the same domain, where the URL is a subpath
of the top window's path, or where the root-relative URL is in the book's list
of component ids.

joseph/Monocle,joseph/Monocle,joseph/Monocle,rethinkbooks/Monocle,rethinkbooks/Monocle,rethinkbooks/Monocle