sequences.extras: cleanup, make reverse-as faster.
sequences.extras: cleanup, make reverse-as faster.

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