Implement collapsing margin
Adjust top_offset when top margin of a element collapses with its first child
Add reftest for margin collapsing
Fix infinite loop bug.
Make the global object be the Window object. Fixes #833.
auto merge of #759 : ILyoan/servo/collapsing, r=metajack

A part of implementation for CSS 8.3.1 Collapsing margins.
auto merge of #883 : jdm/servo/newglobal, r=kmcallister

Requires https://github.com/mozilla-servo/rust-mozjs/pull/34.
Add css module to use border-style
Add style field to render them in RenderContext
auto merge of #882 : sammykim/servo/infinite-loop, r=metajack

To reproduce:

```html
<span style="font-size: 128px">abc</span>
```
Add some dom node tree implementations
Add node.removeChild
Add AncestorIterator by jgraham
Add node.appendChild
Add apply_border_style to apply each CSSBorderStyle
Update submodules
Add more test codes for border-style. And remove a file for same test
auto merge of #880 : ILyoan/servo/appendChild, r=jdm
auto merge of #811 : sammykim/servo/border-style, r=metajack

As I commented in codes, there are some issues to render some border-styles. I can't figure out why this code doesn't show what I expect. I compare this result with firefox. And when I tested it with CSSBorderStyleDashed, It looks almost same with firefox.
But CSSBorderStyleSolid and CSSBorderStyleDotted don't show right result.
I guess the first problem is processing JoinCap with CSSBorderStyleSolid. It might be problems in Azure or somewhere I don't know exactly.
I suspect the second problem is processing DashPattern with CSSBorderDotted. It is also somewhere in Azure or another modules.
So I sent this PR and expect someone can help me to figure out what the problem makes this issues.
If you can't catch what the problem is exactly, I will leave an issue and look it more after this merged.

PS. I referred to firefox code for border style codes.
URL : http://mxr.mozilla.org/mozilla-central/source/layout/base/nsCSSRenderingBorders.cpp#1080
Remove old lint mode annotation.