Merge pull request #1 from artillery/mark-box2d-rebuild

MICAH: box2d rebuild on OS X
Backport the fix at http://box2d.org/forum/viewtopic.php?f=4&t=7796 into this build of Box2D
Rebuild box2d.js
Merge pull request #2 from artillery/mark-bugfix-backport

MICAH: Backport a Box2D bugfix
Consider collision masks in the b2BroadPhase
Remove code that is now unsupported because of broadphase filtering.
Merge pull request #3 from artillery/mark-broadphase-filter

STEVEARC/MICAH/JONO: Massive speed-up for high unit count situations.
Rebuild box2d.js