Multiple display list support
layout: Use the concurrent hash map for the leaf sets.

64% improvement in style recalc.
Implement document.compatMode

Spec:
http://dom.spec.whatwg.org/#dom-document-compatmode

This is a sub-task for #1428.
auto merge of #1579 : ibnc/servo/multiple_display_lists, r=larsbergstrom

Fixes: #1538

Still needs to be rebased.
layout: Consolidate passes in the sequential path that were consolidated
in the parallel path.
auto merge of #1598 : pcwalton/servo/sequential-mirrors-parallel, r=larsbergstrom

in the parallel path.

r? @larsbergstrom
auto merge of #1600 : pcwalton/servo/use-concurrent-hash-map, r=larsbergstrom

64% improvement in style recalc.

r? @larsbergstrom
Failed to link -lpng while make reftest is fixed.
auto merge of #1599 : brunoabinader/servo/document-compatmode, r=Ms2ger

Spec:
http://dom.spec.whatwg.org/#dom-document-compatmode

This is a sub-task for #1428.
auto merge of #1603 : xiongmao86/servo/master, r=larsbergstrom

I failed at make check, and find the problem in check.mk
Change the inline_border test to use a PNG and regenerate baseline to work on OSX
Give up and set the initial size to be the same as the default size for reftests
Use synchronous image loading for ref test baseline writing