sort: avoid overflow in pivot calculation. thanks to snilsson@nada.kth.se for the original CL.
sort: avoid overflow in pivot calculation.
thanks to snilsson@nada.kth.se for the original CL.

R=gri
CC=golang-dev, snilsson
http://codereview.appspot.com/3280044

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