SAN FRANCISCO - Paul A. Flaherty, a computer engineer who helped create the pioneering AltaVista online search engine, has died. He was 42. Flaherty died March 16 of a heart attack at his home in Belmont, about 20 miles south of San Francisco, family members said Friday. Flaherty came up with the idea of indexing Web pages that made the AltaVista search engine one of the most popular Internet search tools in the mid-1990s.