test_slam_layout, a new layout perf test case
Stop rendering when script queries layout
Address review comments
Refactor document damage to distinguish it from layout/style damage.

Also, standardize on the name "reflow" instead of "relayout" or "build".
Use the scroll hack
Roll up block layout changes
Only warn, don't assert, if the node range length is zero.

This broke http://www.all-about-ferrets.com/long-tailed-weasel.html
Update the configure script to pass --enable-64bit
Address review comments
merge conflicts