go/doc: remove os.NewError anti-heuristic
go/doc: remove os.NewError anti-heuristic

It will be obsolete when error happens.

Submitting this now will make the error transition earlier,
at the cost of making a locally-built godoc viewing
/pkg/syscall or /pkg/os have some functions appear
under the Error type as constructors.

R=golang-dev, adg
CC=golang-dev
http://codereview.appspot.com/5305067

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang