Fixed jQuery 1.2.6 mouseleave issue from #920.

Use bind, rather than .mouseleave, because we officially still support
jQuery 1.2.6, which doesn't define a shortcut for mouseenter or
mouseleave.  This was a bug/oversight that was fixed somewhere around
1.3.x.  We can return to using .mouseleave when we drop support for
1.2.6.