Fix to avoid attribute name clash between Document/HTMLDocument

Use children() instead of traverse_preorder(), and avoid having
GetHead() in both Document and HTMLDocument.

Closes #1465.
auto merge of #1472 : brunoabinader/servo/document-head, r=jdm

Use children() instead of traverse_preorder(), and avoid having
GetHead() in both Document and HTMLDocument.

Closes #1465.
Update UA stylesheets for lists
Upgrade to latest Rust.
auto merge of #1473 : metajack/servo/rustup-20131219, r=jdm
auto merge of #1478 : recrack/servo/useragentcss, r=SimonSapin

#1232

Servo UA (http://www.w3.org/TR/CSS21/sample.html)

This is UA css from http://mxr.mozilla.org/mozilla/source/layout/style/html.css and http://dev.w3.org/csswg/css-lists/#ua-stylesheet

```
ul margin-left: 40px -> padding-left: 40px
ol margin-left: 40px -> padding-left: 40px
```
Remove needless code.

This `OK(())` should be propagated from `Element.set_attribute()`.
Split up the utility function to make internal attribute's namespace.
Enable only remove operation for Document::update_idmap().
Add the comment to explain the dual declaration.
Implement Element.removeAttribute()/removeAttributeNS().
auto merge of #1448 : saneyuki/servo/attr, r=jdm
Remove unused imports.
auto merge of #1481 : Ms2ger/servo/unused-imports-2, r=metajack
add names for all servo spawned tasks

* add servo_util::task::{spawn_named,spawn_with_named} functions

* add name param for spawn_listener and spawn_conversation functions

this should resolve #1169
Enable checks for reftest exit status.
auto merge of #1484 : metajack/servo/check-reftest-status, r=larsbergstrom

r? @larsbergstrom
Implement Document::doctype

Closes #1482.
auto merge of #1457 : zmike/servo/master, r=jdm

this should resolve #1169
auto merge of #1483 : brunoabinader/servo/document-doctype, r=jdm

Closes #1482.