Use CSS3 box-shadow property for Cart tooltip

Use CSS3 box-shadow property for Cart tooltip

The OPAC Cart tooltip ("Your cart is empty," "1 item(s) added to your
Cart") currently uses a jQuery plugin to generate a drop shadow.
This works cross-browser, but has a high failure rate with regard
to hiding the shadow consistently, resulting in an orphan shadow
after the tooltip has been hidden. I propose to instead use the
new CSS3 property "box-shadow" (-moz-box-shadow and -webkit-box-
shadow for FireFox and Safari/Chrome). Currently Internet Explorer
does not support this property. I think this is an
acceptable tradeoff for more stable functionality.

Signed-off-by: Galen Charlton <gmcharlt@gmail.com>