Forcibly close tooltips if :hover is missing.

Some browsers (***ing IE7) don't have the ':hover' pseudo-class. In this
case, tooltip windows will be left open until the user mouse overs them.

This branch just closes the tooltip if the ':hover' pseudo-class is
missing.
Merge branch 'master' into ie7
Avoided using the :hover pseudo-class for IE7 compatibility.

This implements a mouseover / mouseleave solution. It appears to work on
IE6 & up. (The code is much uglyier, though.)