effective_go: clarified small comment
effective_go: clarified small comment

R=rsc, cw
CC=golang-dev
http://codereview.appspot.com/217085

nightlyone/golang,ssrl/go,pombredanne/go-deleteme,tv42/old-go,gnanderson/go,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,gnanderson/go,bdwalton/debian-golang,pombredanne/go-deleteme,dsriram/golang,gnanderson/go,dsriram/golang,nightlyone/golang,ssrl/go,tianon/debian-golang,nightlyone/golang,apparentlymart/golang,bdwalton/debian-golang,tianon/debian-golang,tv42/old-go,gnanderson/go,tianon/debian-golang,pombredanne/go-deleteme,bdwalton/debian-golang,nightlyone/golang,nightlyone/golang,ssrl/go,tv42/old-go,pombredanne/go-deleteme,ssrl/go,nightlyone/golang,tianon/debian-golang,h8liu/golang,dsriram/golang,pombredanne/go-deleteme,dsriram/golang,pombredanne/go-deleteme,gnanderson/go,ssrl/go,pombredanne/go-deleteme,tv42/old-go,nightlyone/golang,bdwalton/debian-golang,h8liu/golang,h8liu/golang,apparentlymart/golang,bdwalton/debian-golang,tianon/debian-golang,tianon/debian-golang,tv42/old-go,h8liu/golang,tianon/debian-golang,bdwalton/debian-golang,bdwalton/debian-golang,bdwalton/debian-golang,gnanderson/go,dsriram/golang,ssrl/go,apparentlymart/golang,dsriram/golang,dsriram/golang,h8liu/golang,apparentlymart/golang,tianon/debian-golang,h8liu/golang,gnanderson/go,ssrl/go,tv42/old-go,h8liu/golang,tv42/old-go