Billionaire investor Carl Icahn gave Greenbrier (GBX) shares a jolt Tuesday with notice he was part of a team taking a 9.99% stake in the railcar manufacturer. According to a Securities and Exchange Commission filing, Icahn sees the shares as undervalued. He also may be interested in revisiting the failed 2008 bid to merge Greenbrier with his American Railcar Industries (ARII). The filing notes that Icahn has notified Greenbrier he wants to talk