[dom] Pull Request: Make two loops to adopt a node

nox has just submitted a new pull request for 
https://github.com/whatwg/dom:

== Make two loops to adopt a node ==
@Ms2ger pointed out to me that the fix introduced in #66 is less than 
perfect, because the unsuspecting loop over node's inclusive 
descendants mean running their adopting steps in a tree of which nodes
 are owned by two different documents.

See https://github.com/whatwg/dom/pull/71