fixed issue in calculation of top. Probably due to new version of Jquery.

…e.g. for table cells), incl. test

…isibility: hidden closes the calendar - target is the root node instead of the button.

rather than checking if any tooltips already exist.
this way tooltips on some elements that are reloaded via
ajax calls will continue working. the previous code would
assume all tooltips still exist if *any* of the tooltips still
exist -- even if some of them no longer exist. now, part of a
page may be changed and can have new tooltips created instead
of only the ones for elements that did not change.

resolves: #349

Signed-off-by: Adam Mckaig <adam.mckaig@gmail.com>

… right after. Enables chaining using the onClose callback method