Use `Any` for the layout data.

Breaks the dependency between `gfx` and `script`, which is nice.
Introduce jsid_to_str to simplify jsval_to_str callers that have an id.
Simplify InterfaceObjectToString.
Rewrite jsval_to_str and introduce jsval_to_domstring.
Add some basic debug info for dumping flows.
auto merge of #1212 : larsbergstrom/servo/dump_flows, r=brson

With @ryanhc

Will add more debugging information for RenderBoxes in InlineFlows and `dump_str` for each of the RenderBoxes later.
Add a spec-incompliant load event.
auto merge of #1206 : Ms2ger/servo/strings, r=jdm

I'll probably do a followup to actually pass non-nullable strings to the native functions.
Make --enable-debug turn on full debugging information, and --disable-optimize disable all optimizations.
fix #1211: for table-related elements, handle temporarily as 'block' display intead of 'inline' display
auto merge of #1216 : june0cho/servo/temp_fix_tableflow, r=kmcallister

In order to fix the wikipedia error, I temporarily change the display property of table-related elements to 'block' instead of 'inline'.
When table is implemented, it should be changed to proper value.

@sonwow
@brson
auto merge of #1214 : jdm/servo/gdbready, r=larsbergstrom

...timize disable all optimizations.
Initial support for Attr and namespaces.
auto merge of #1213 : jdm/servo/loadevent, r=kmcallister

It's good enough for now, since we don't track document resources at all. Should be good enough for #841.
auto merge of #1218 : jdm/servo/attr, r=kmcallister
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.