maps access to a missing key will return the "zero" value
maps access to a missing key
will return the "zero" value

R=rsc
CC=golang-dev
http://codereview.appspot.com/700041

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