Created by: coreyti
prefixing placement with "sibling" will insert the tooltip before the source element, and position it based on the source element's position relative to its offset parent.
this change allows for tooltips that will remain properly positioned on window resize & content change, without inserting the tooltip "in" the element, which would be invalid for <input> source elements, for example.
a closed issue that this change should resolve: https://github.com/twitter/bootstrap/issues/3067