spec: define that initialization is sequential
spec: define that initialization is sequential

This is true of the existing implementations, and I think
it is an important property to guarantee.

R=golang-dev, r, borman, r
CC=golang-dev
http://codereview.appspot.com/5321058

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