runtime: fix complex division benchmarks we can't add the division result to n during iteration, because it might turn n into NaN or Inf.
runtime: fix complex division benchmarks
we can't add the division result to n during iteration, because it might
turn n into NaN or Inf.

R=golang-dev, rsc, iant, iant
CC=golang-dev
http://codereview.appspot.com/6197045

wesolows/golang,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang,firebitsbr/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang,wesolows/golang-old,wesolows/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang,wesolows/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang-old