Remove render backend option as it doesn't work and confuses people.
auto merge of #3711 : glennw/servo/cleanup-opts, r=pcwalton

r? @pcwalton @metajack
Use opts as a global, to avoid cloning and passing the struct all over the code.
auto merge of #3729 : glennw/servo/opts-cleanup, r=mbrubeck
Fixes the table_percentage_width_a.html reftest with incremental reflow turned on.
auto merge of #3715 : cgaebel/servo/fix-table-percentage-width, r=pcwalton

This also enables incremental reflow by default. \o/

r? @pcwalton
Update rust-cssparser to revision required by cssom branch.
auto merge of #3745 : glennw/servo/update-cssparser, r=jdm

r? @jdm
Update rust-core-text, handle empty font collections. Fixes #3703.
auto merge of #3750 : glennw/servo/fix-3703, r=pcwalton

r? @pcwalton @metajack