bluestork/shutterstock.com Karen Aitchison, a senior who has shopped the Diamond Heights Boulevard Safeway for 30 years, lives three flights up. When her grocery store stopped stocking paper bags with handles last month, she did what any sensible person would do — she hoarded the old ones and started reinforcing them with strapping tape. Her alternatives, she told SFGATE reporter Susana Guerrero by email , are $7 reusable bags so heavy they add to the load, or cloth bags that flop awkwardly on the stairs. Safeway swapped in handleless paper bags across all 13 of its San Francisco stores sometime in April, and weeks later, they're still the default. SFGATE checked on Monday and found the new bags everywhere; a few locations had a sleeve or two of the old style behind the counter, and one Marina Boulevard clerk said his store had run through them. The 7th Avenue store thinks it might get more sometime this month, no promises.…