twitter/bootstrap — pull request #5184 by advancedrei (2012-09-18 14:57:30+00:00)
Title: Support for left-opening dropdown submenus

Adds a new class called .dropdown-submenu-left. It is useful when you
have a .pull-right DropDown that has submenus. Without this, the menu
opens left past the page boundary, which can trigger the scrollbars and
cause other nastiness.

Resubmitting per https://github.com/twitter/bootstrap/pull/5156