Added Node's query_selector_all helper function
Implement support for ParentNode's querySelectorAll
Added ParentNode's querySelectorAll content tests
Use interior mutability for MouseEvent.
auto merge of #2632 : brunoabinader/servo/document-queryselectorall, r=Ms2ger

Spec:
http://dom.spec.whatwg.org/#dom-parentnode-queryselectorall

Closes #851.
Use internal mutability for Document::idmap.
Pass immutable self to Node::{SetNodeValue, SetTextContent}.
Pass immutable document to parse_html.
Cleanup a mutable variable in dispatch_event.
Pass immutable self to HTMLBodyElement::SetOnunload.
auto merge of #2640 : Ms2ger/servo/derefmut, r=jdm
Use downloaded snapshots instead of in-tree rust. Also a working linux travis conf