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

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