Summer concerts in the city are frequently revealing in their own several ways. A quick look around Davies Hall last Friday would have reminded locals that there is no need to escape San Francisco in July. Many of the regular faces were present, and so, too, were throngs of young couples in from the suburbs. In the shirt-sleevy dusk, Van Ness Avenue and its many venues seemed the focal point of date night. The line for will-call tickets snaked around the block.