misc/benchcmp: don't require "Benchmark" at beginning of line
misc/benchcmp: don't require "Benchmark" at beginning of line

Output is package_name.BenchmarkXXX.

R=rsc
CC=golang-dev
http://codereview.appspot.com/5440123

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