Any eBay shareholders who were less than thrilled about eBay's $1.2 billion acquisition of Gmarket last June may feel better after hearing about a new plan that involves the property. eBay announced late yesterday that it intends to work with Gmarket's founder to expand Gmarket's presence in Japan and Singapore. This won't be entirely eBay's show; the effort will come in the form of a fresh joint venture in which eBay will have a 49 percent stake. Young Bae Ku,