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.
Fix HTMLImageElement setters.

These would crash because the functions they call assert that they receive
lower-case names.

Fixing the crash allows reflection-embedded.html to finish successfully.
make Node.type_id field private
Add prerequisites for Arch Linux to the readme.
Merge pull request #3222 from Ms2ger/img-reflection

Fix HTMLImageElement setters; r=jdm
Merge pull request #3224 from duncankl/readme-arch-linux-setup

Add prerequisites for Arch Linux to the readme; r=Manishearth
Add a note about autoconf 2.13.

Many people seem to have this question.
Merge pull request #3225 from Ms2ger/note-autoconf

Add a note about autoconf 2.13; r=Manishearth
Disable intermittently failing Document-characterSet-normalization.html (fixes #3209).

As we currently don't support anything but utf-8, this is not a particularly
useful test to run.
Merge pull request #3210 from seanmonstar/private-node-type-id

make Node.type_id field private, access through type_id()
Merge pull request #3226 from Ms2ger/3209-disable

Disable intermittently failing Document-characterSet-normalization.html (fixes #3209); r=jdm
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
Implement TreeWalker