twbs/bootstrap — pull request #10625 by chrisege (2013-09-13 19:32:49+00:00)
Title: fix for scrollbar 'hop' on .modal-open

this fixes #9855.

It uses the same technique that Twitter uses on their own modals:

create two empty divs, one scrolling within the other. The difference in widths is the offset needed to stop the body from shifting when its scrollbar is hidden.