This implements the DOM tree accessors that return a HTMLCollection
Fix some implementations for DOM tree accessors
Factor out CSS length to Au conversion
auto merge of #659 : sonwow/servo/dom, r=jdm

Basic implementation about DOM tree accessors in HTMLDocument.
(image, embeds, plugins, links, forms, scripts, anchors, applets)
auto merge of #663 : sanxiyn/servo/from-length, r=metajack
Simplify HTMLCollection predicates
auto merge of #666 : kmcallister/servo/htmldocument, r=jdm
Fill out various proxy binding traps as part of making setters work. Add named getter and setter and indexed getter support, as well as proxy object expandos. Fixes #660.
Implement clear
Update submodules
Generate bindings for Node, CharacterData, Text, Element, and HTMLElement. Hook up text nodes to use the new bindings.
Generate bindings for HTMLHeadElement.
Generate HTMLHtmlElement bindings.
auto merge of #672 : jdm/servo/proxysetter, r=metajack

... named getter and setter and indexed getter support, as well as proxy object expandos. Fixes #660.
Generate bindings for HTMLAnchorElement.
auto merge of #673 : sanxiyn/servo/clear, r=metajack
Place float children of floats correctly in the flow tree.
Fix the handling of flow_contexts in floats.

The num_floats was hard-coded to 1 and didn't take into account the
children. Also the float context was not being threaded through the children
properly.
auto merge of #676 : metajack/servo/acid1-all-boxes, r=eric93

This makes acid1 have all 6 boxes show up, and almost correctly positioned.

r? @eric93
Remove broken forward declaration.