spec: &x panics if x does
spec: &x panics if x does

See golang.org/s/go12nil for the extended version.

R=golang-dev, r, adonovan
CC=golang-dev
https://codereview.appspot.com/12964043

pombredanne/go-deleteme,tv42/old-go,tv42/old-go,pombredanne/go-deleteme,apparentlymart/golang,apparentlymart/golang,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,tv42/old-go,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,tv42/old-go,pombredanne/go-deleteme,tv42/old-go,tv42/old-go,pombredanne/go-deleteme,apparentlymart/golang,apparentlymart/golang,pombredanne/go-deleteme