Cornerstone Books, a 3,000-square-foot bookstore/cafe in historic Salem, Massachusetts, celebrated its grand opening Wednesday with a visit from the town's mayor to cut the ribbon, an evening of live entertainment from the Squatcho Bondo Band of Gloucester, and food and drink for all. The store, owned by Gilbert Pili, managed by his brother Erik, with old friend Dan Johnson doing the buying, has long been a gleam in Pili's eye. But for many months, Cornerstone's opening was bedeviled by impediments of all sorts.