os: be explicit in the package comment that this package is for portable features only.
os: be explicit in the package comment that this package is for portable features only.

R=golang-dev, rsc
CC=golang-dev
http://codereview.appspot.com/4602058

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