layout: Make "height" relative to the initial containing block for the root.

Fixes Wikipedia.
layout: Change `~Box` to `Box`.

63% improvement in box building on the rainbow page.
auto merge of #1371 : pcwalton/servo/flatten-box, r=larsbergstrom

63% improvement in box building on the rainbow page.

r? @larsbergstrom
make font/platform/gfx/font_context safe
remove @ in LayoutTask.FontContext
makes linux/Arc<FontContextHandle> Rc<FontContextHandle>
auto merge of #1372 : ksh8281/servo/remove_@_in_LayoutTask.FontContext2, r=pcwalton

Remove @ in layout task.font_context & fix linux/FontContextHandle
Arc<FontContextHandle> -> Rc<FontContextHandle>
Remove obsolete makefile lines about Netsurf’s libcss.
Add rust-encoding as a submodule.

Upstream: https://github.com/lifthrasiir/rust-encoding
Servo’s fork: https://github.com/mozilla-servo/rust-encoding

As of this writing, upstream’s master branch targets Rust 0.8,
and its rust-0.9-pre branch targets Rust master.
Servo uses a Rust version in-between those.
I pushed a rust-servo branch to our fork
that backports from rust-0.9-pre.
Add support for non-UTF8 CSS stylesheets, with rust-encoding.
Make sure stylsheets have a base URL.
Merge pull request #1370 from pcwalton/height-containing-block

layout: Make "height" relative to the initial containing block for the root.
Merge pull request #1368 from SimonSapin/master

Fix #1264: support namespaced attribute selectors.
net: Color space convert 32-bit ARGB PNGs as well.
Merge pull request #1379 from pcwalton/png

net: Color space convert 32-bit ARGB PNGs as well.
test: Add missing line in reftest list. rs=sillytestfix
layout: Don't delete non-text boxes from the list of input boxes when
flushing text clumps. Fixes this page:

    http://en.wikipedia.org/wiki/Yellow_River

This is not the most efficient thing to do; a FIXME has been added
noting what is most correct.
auto merge of #1381 : pcwalton/servo/bogus-box-deletion, r=jdm

flushing text clumps. Fixes this page:

    http://en.wikipedia.org/wiki/Yellow_River

This is not the most efficient thing to do; a FIXME has been added
noting what is most correct.

r? @jdm
contenttest: Print stderr
Kill Servo instead of displaying about:failure when running content tests

Fixes #1380.