Use `Any` for the layout data.

Breaks the dependency between `gfx` and `script`, which is nice.
impl window self
Fix the crash on #582. Combining characters are still not shown because this is not implemented. With @sonwow
Make DOMString represent a non-nullable string.
Don't pass nullable strings to native DOM methods that want non-nullable strings. Fixes #1207.
Update test to code changes.
auto merge of #1215 : Ms2ger/servo/DOMString-nonnull, r=jdm
Rewrite replace_all.
auto merge of #1222 : jdm/servo/remove_all, r=jdm
Implement Element.attributes.
Implement a missing step in the node 'insert' algorithm.
auto merge of #1225 : Ms2ger/servo/insert-docfrag, r=jdm
auto merge of #1220 : jdm/servo/attrlist2, r=metajack
layout: Add debug strings for float flows and boxes
auto merge of #1227 : pcwalton/servo/debug-more, r=kmcallister

r? @larsbergstrom
auto merge of #1208 : pcwalton/servo/any-layout-data, r=metajack

Breaks the dependency between `gfx` and `script`, which is nice.

This exposed some performance issues with Rust's `Any` type, which I've filed:

https://github.com/mozilla/rust/issues/10382
Make list-item's display style block
Rename main/layout/aux.rs -> main/layout/extra.rs. (#1226)
Cleanup attribute setting functions a bit.
Make Attr::local_name always initialized.