Prot# IM101042: A Phse IIB, Mlt-Cntr, Rndmzd, Dbl-Blnd, Plcb-Cntrlld Stdy to Evlt the Effccy & Sfty of Abatacept vs. Plcb on A Bckgrnd of Orl Glucocorticosteroids in the Trtmnt of Sbjcts w/ Systmc Lupus Erythematosus & the Prvnton of Sbsqnt Lupus Flare