Uses carefully chosen CSS that styles the search bar correctly on both Fedora Core 15 (with Gtk+ 3.0) and Ubuntu Oneiric (with Gtk+ 3.2). Mostly closes #3873. The outstanding problem involves the "prelight" or "hover" state of the search bar buttons. This state appears unresponsive to styling using either the CSS or legacy APIs. I'll be in communication with some of the Gtk+ devs over the next few days to see how we can force this state to by styled.