hash-sets: speed up union on two hash-sets.
hash-sets: speed up union on two hash-sets.

mrjbq7/factor,factor/factor,slavapestov/factor,dch/factor,AlexIljin/factor,mrjbq7/factor,factor/factor,bpollack/factor,slavapestov/factor,AlexIljin/factor,dch/factor,bpollack/factor,slavapestov/factor,bjourne/factor,sarvex/factor-lang,nicolas-p/factor,tgunr/factor,dch/factor,mrjbq7/factor,nicolas-p/factor,bpollack/factor,factor/factor,nicolas-p/factor,sarvex/factor-lang,bjourne/factor,bpollack/factor,nicolas-p/factor,bpollack/factor,mrjbq7/factor,nicolas-p/factor,AlexIljin/factor,factor/factor,dch/factor,mrjbq7/factor,sarvex/factor-lang,dch/factor,tgunr/factor,factor/factor,dch/factor,slavapestov/factor,bjourne/factor,bjourne/factor,bpollack/factor,sarvex/factor-lang,nicolas-p/factor,AlexIljin/factor,AlexIljin/factor,bjourne/factor,bpollack/factor,slavapestov/factor,factor/factor,bjourne/factor,bjourne/factor,nicolas-p/factor,sarvex/factor-lang,slavapestov/factor,sarvex/factor-lang,AlexIljin/factor,slavapestov/factor,mrjbq7/factor,tgunr/factor,tgunr/factor,sarvex/factor-lang,AlexIljin/factor,tgunr/factor,tgunr/factor