MADONNA and pal Rosie Perez sent fellow diners at a San Francisco cafe ducking for cover after the Material Girl started a food fight by telling her feisty lunch partner she ate like a pig. ''You know, for an actress, you eat like a pig!'' Madonna was reported to have said. Do you know who was the first black violinist? Violins have been around for more than 400 years, so we don't know all the people who may have played. That said, there were some early and outstanding people of African descent who played and composed for the violin. The earliest we know of was Chevalier de Saint-Georges, born in Guadeloupe in 1739. His mother was African and his father French. George Bridgetower, a child prodigy, was born in 1778. His father was African. Beethoven wrote the Kreutzer Sonata for Bridgetower, who debuted the work.