From People Longtime lovebirds Robert Pattinson and Kristen Stewart made a rare semi-public appearance together during the Oscar weekend in Los Angeles.  The couple attended WME's Grey Goose-hosted pre-Oscar bash at agent Ari Emanuel's house and were "quite affectionate" in front of other revelers, a source says. Adds the source: "[They] seemed very comfortable and sweet with each other." The d…