Add a layout debug module. This outputs a trace of the layout process to a JSON
file which can be viewed in an external tool. It provides a timelapse view of
how the flow tree and fragments changed during the layout process, which makes
it easier to debug layout bugs.
Change scope macro to be a no-op in release builds.
Avoid trying to trace a null JSVal.

JSVal::trace_kind() asserts that it is a markable type; null is a gcthing that
is not markable.
Correct the iterator adaptors used in parsing integers (fixes #3208).

This avoids Azure segfaulting trying to set up a 100999px*100999px canvas.

The test still fails due to its use of getComputedStyle.
Merge pull request #3227 from Ms2ger/3208-parse-integer

Correct the iterator adaptors used in parsing integers (fixes #3208); r=jdm+Manishearth
Merge pull request #3240 from Ms2ger/mark-null

Avoid trying to trace a null JSVal; r=jdm
Merge pull request #3206 from glennw/layout-trace-enc

Add an initial pass at a layout debug module.
Fix WPT when /usr/bin/python is python3

Use the Python that was detected during configure.
Merge pull request #3246 from SimonSapin/wpt-python2

Fix WPT when /usr/bin/python is python3
Cargoify servo
Merge pull request #3230 from servo/cargoify

Cargoify servo
Update the README a bit.
Only pass extra link flags on OS X.

Fixes #3249
Merge pull request #3259 from metajack/update-readme

Update the README a bit.
Merge pull request #3260 from metajack/fix-cef-linux

Only pass extra link flags on OS X.
Improve quality of font rendering on Linux (and Android).

The freetype hinting only works on integer pixel sizes. For this
reason, the advance width metrics for a font of size 12.99 are
the same as the advance metrics for a font of size 12.0. This
results in small fonts appearing to overlap slightly, which is
particularly noticeable on parts of Wikipedia. Round the font
size up to a pixel boundary inside the freetype system.

Also fetch the system default fonts for the generic font families
rather than hard coding them.

These two changes make the font rendering on Linux very close
to the Firefox font rendering on Wikipedia.
Define constant parameters strings as statics.
Add glfw3 as a dep to the README.
Add note about installing glfw3 from source.
Merge pull request #3256 from glennw/font-fixes

Improve quality of font rendering on Linux (and Android).