Merge branch '3.0.0-wip' of github.com:twitter/bootstrap into 3.0.0-wip

docs/assets/css/bootstrap.css

@@ -4896,6 +4896,9 @@ a.list-group-item.active > .badge,
      -moz-transition: width 0.6s ease;
        -o-transition: width 0.6s ease;
           transition: width 0.6s ease;
+  -webkit-backface-visibility: hidden;
+     -moz-backface-visibility: hidden;
+          backface-visibility: hidden;
 }
 
 .progress-striped .progress-bar {

less/grid.less

@@ -31,7 +31,7 @@
 .generate-grid-columns(@grid-columns);
 
 // Then generate the larger grid classes via media query
-@media screen and (min-width: 768px) {
+@media screen and (min-width: @screen-small) {
   .generate-large-grid-columns(@grid-columns);
 }
 

less/progress-bars.less

@@ -63,6 +63,7 @@
   background-color: @progress-bar-bg;
   .box-shadow(inset 0 -1px 0 rgba(0,0,0,.15));
   .transition(width .6s ease);
+  .backface-visibility(hidden);
 }
 
 // Striped bars