xref
Rewrite concept-traverse-children. More of Traversal might need rewriting. :-(

Fixes https://www.w3.org/Bugs/Public/show_bug.cgi?id=20445
Define Document's origin. In related news: we now have an HTML dependency.

Fixes https://www.w3.org/Bugs/Public/show_bug.cgi?id=20390
copypasta
TreeWalker nextNode() and previousNode() had bugs too.

Thanks @Krinkle! (Also the last copypasta commit was wrong as it had
previous and next reversed, this fixes that too.)
Define what origin and effective script origin are in various Document contexts. This further intertwines HTML and DOM in not clearly avoidable ways.

Fixes https://www.w3.org/Bugs/Public/show_bug.cgi?id=20390 in a better
way.
Effective script origin should initially be an alias.
Make NodeIterator.detach() completely useless. Just like Range.detach().

See also https://bugzilla.mozilla.org/show_bug.cgi?id=823549
Adopt a node into a document first and then do base URL fixup.

Fixes https://www.w3.org/Bugs/Public/show_bug.cgi?id=20492
typo
RootNode -> ParentNode. The people got confused.
Consistify. No normative change.