go spec: clarify return statement rules
go spec: clarify return statement rules

Added example of a return statement w/o expressions
in a function with a _ result parameter.

See also: http://code.google.com/p/go/issues/detail?id=1586

R=rsc, r, iant
CC=golang-dev
http://codereview.appspot.com/4266049
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go