layout: Rewrite the float context.

This rewrites the float context to avoid dynamic failures resulting from
`.clone()` misuse. It also renames the float context to the simpler
`Floats`. The new version is modeled on WebKit's `FloatingObjects`.
Remove no-op implementations from Element and add some spec links.
auto merge of #1774 : Ms2ger/servo/element-noops, r=jdm
layout: Stop racing on the JSManaged borrow flags
auto merge of #1772 : pcwalton/servo/borrow-flags-race, r=jdm

r? @jdm
auto merge of #1770 : pcwalton/servo/rewrite-float-context, r=kmcallister

This rewrites the float context to avoid dynamic failures resulting from
`.clone()` misuse. It also renames the float context to the simpler
`Floats`. The new version is modeled on WebKit's `FloatingObjects`.

r? @kmcallister
Build Fontconfig 2.11 in-tree on Linux

After applying this patch, on Linux you will need to

    ../configure
    make clean-rust-azure clean-fontconfig clean-rust-fontconfig

Fixes #1752.
Renamed HTMLIframeElementTypeId to HTMLIFrameElementTypeId
Install expat-devel on Linux builders
Add url getter to Page and fix users of Page url with it.(fixes #1762)
auto merge of #1776 : lpy/servo/issue1762, r=jdm

see #1762
Move Error, Fallible, ErrorResult out of utils.rs (fixes #1749)
auto merge of #1773 : sawrubh/servo/issue1749, r=Ms2ger
Implement "resize" DOM Event.

* We cannot automate this feature.
* So this testcase is a manual test.
auto merge of #1783 : saneyuki/servo/resize, r=jdm

#1715
auto merge of #1781 : hgentry/servo/mozilla-servo, r=metajack

Simple change. I hope I'm using github correctly; I'm not too familiar with the PR system. Fixes #1777.
De-@mut the script crate.
auto merge of #1755 : jdm/servo/demut, r=jdm,metajack

Requires https://github.com/mozilla-servo/rust-mozjs/pull/49.
Install gperf on Linux builders
Work around missing expat.pc on some RedHat-based systems