simple-flat-file: add back string interning.
simple-flat-file: add back string interning.

tgunr/factor,AlexIljin/factor,bpollack/factor,mrjbq7/factor,bpollack/factor,tgunr/factor,factor/factor,mrjbq7/factor,bpollack/factor,tgunr/factor,AlexIljin/factor,bpollack/factor,factor/factor,mrjbq7/factor,mrjbq7/factor,bpollack/factor,AlexIljin/factor,mrjbq7/factor,AlexIljin/factor,AlexIljin/factor,tgunr/factor,tgunr/factor,AlexIljin/factor,tgunr/factor,factor/factor,factor/factor,factor/factor,AlexIljin/factor,bpollack/factor,bpollack/factor,factor/factor,mrjbq7/factor