A DEADLY MEASLES EPIDEMIC in Philadelphia claimed its sixth victim Friday, a 19-month-old boy whose mother does not believe in modern medicine, health officials said . . . SIX PEOPLE were killed in an avalanche Friday in Switzerland's worst ski accident this winter. The avalanche occurred in the Valais Alps in southern Switzerland. Authorities had earlier warned that mild weather conditions increased the risk of avalanches . . . REPUTED MOBSTER Louis "Streaky" Gatto Sr. is fit to stand trial on racketeering charges, a federal judge ruled Friday in Newark, N.J. U.S. District Judge Harold Ackerman rejected defense claims that Gatto's forgetfulness and incontinence have left him unable to answer the charges.