Don't require root pipeline to match new pipeline

This reverts 2b0134be7bb8a4372f1a8703b5a1b114e65351f6 because it was
not correct for iframes.
Implement TElement for JSRef<Element>
Implement TNode for JS<Node>
Added ParentNode.querySelector skeleton
Implement querySelector for Document
Implement querySelector for DocumentFragment
Implement querySelector for Element
Added content tests for querySelector
Fix and disable some compile warnings.
Add an issue number to a FIXME comment.
Bonus: Make Reflector::object private.
Fix leak

Introduced by yours-truly in 7212c3573e7f2b13f907e17a5683d382b34ab932

Oopsie.
auto merge of #2606 : Ms2ger/servo/warnings, r=jdm
auto merge of #2603 : mbrubeck/servo/units, r=pcwalton

This is a rebased, squashed, and updated version of #2444.
Fixed traversal issues
auto merge of #2591 : brunoabinader/servo/document-queryselector-v3, r=jdm

This is a subtask for #2254 & #2576.

Spec:
http://dom.spec.whatwg.org/#dom-parentnode-queryselector
auto merge of #2607 : bjz/servo/leeeeeak, r=jdm

Introduced by yours-truly in 7212c3573e7f2b13f907e17a5683d382b34ab932

Oopsie.
auto merge of #2602 : mbrubeck/servo/revert-root-pipeline-check, r=pcwalton

This reverts 2b0134be7bb8a4372f1a8703b5a1b114e65351f6 because it was not correct for iframes.  Oops.  (Wasn't caught by tests because we still have other crashes preventing iframe testing.)  r? @pcwalton.
    Allow union types to be used as return values
auto merge of #2573 : Manishearth/servo/union-return, r=Ms2ger

Blocks #2559