pidigits: Remove TODO, minor improvements
pidigits: Remove TODO, minor improvements

I tried adding a Scale method to big.Int and it didn't make any noticeable
difference, so I'm removing my TODO.

Also got rid of a few obvious allocations that I missed earlier for a modest
improvement (~5%).

R=golang-dev, gri
CC=golang-dev
http://codereview.appspot.com/2711043

Committer: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>

pombredanne/go-deleteme,tv42/old-go,gnanderson/go,dsriram/golang,dsriram/golang,apparentlymart/golang,gnanderson/go,ssrl/go,dsriram/golang,h8liu/golang,ssrl/go,apparentlymart/golang,tv42/old-go,pombredanne/go-deleteme,apparentlymart/golang,dsriram/golang,tv42/old-go,tv42/old-go,gnanderson/go,pombredanne/go-deleteme,gnanderson/go,tv42/old-go,apparentlymart/golang,gnanderson/go,ssrl/go,pombredanne/go-deleteme,h8liu/golang,pombredanne/go-deleteme,h8liu/golang,ssrl/go,pombredanne/go-deleteme,gnanderson/go,dsriram/golang,h8liu/golang,h8liu/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,dsriram/golang,ssrl/go,ssrl/go,tv42/old-go,dsriram/golang,ssrl/go,pombredanne/go-deleteme,tv42/old-go,h8liu/golang,h8liu/golang,gnanderson/go