Tooltips aren't centered

[danvk]

e.g. on the biodalliance.org page, when I hover over the "<<":

It's fine if the tooltip can't escape the containing <div>. But the nub on top of the tooltip should always point at the button that the tooltip is describing.

[dasmoth]

This may be tricky to resolve without re-engineering the Bootstrap-based tooltips -- but agree that the current ones look quite strange if they get "shifted".