cmd/gc: change compile error to "use of package %S without selector"
cmd/gc: change compile error to "use of package %S without selector"

At present, when a package identifier is used outside of a selector expression, gc gives the error "use of package %S outside selector". However, in the selector expression x.f, the spec defines f as the selector. This change makes the error clearer.

Fixes issue 7133.

LGTM=rsc
R=golang-codereviews, rsc
CC=golang-codereviews
https://codereview.appspot.com/50060047

Committer: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

rdp/rogerpack2005-golang,webfd/go-zh,glycerine/jeaten-go-arrayof-structof,sanjosh/sanjos100-tipc,bryanxu/go-zh,d0f/go-zh,d0f/go-zh,glycerine/jeaten-go-arrayof-structof,sanjosh/sanjos100-tipc,d0f/go-zh,rdp/rogerpack2005-golang,webfd/go-zh,glycerine/jeaten-go-arrayof-structof,bryanxu/go-zh,bryanxu/go-zh,sanjosh/sanjos100-tipc,sanjosh/sanjos100-tipc,webfd/go-zh,sanjosh/sanjos100-tipc,d0f/go-zh,rdp/rogerpack2005-golang,d0f/go-zh,glycerine/jeaten-go-arrayof-structof,d0f/go-zh,rdp/rogerpack2005-golang,webfd/go-zh,webfd/go-zh,bryanxu/go-zh,rdp/rogerpack2005-golang,sanjosh/sanjos100-tipc,glycerine/jeaten-go-arrayof-structof,d0f/go-zh,webfd/go-zh,glycerine/jeaten-go-arrayof-structof,bryanxu/go-zh,rdp/rogerpack2005-golang,bryanxu/go-zh,rdp/rogerpack2005-golang,bryanxu/go-zh,webfd/go-zh,sanjosh/sanjos100-tipc,bryanxu/go-zh,glycerine/jeaten-go-arrayof-structof,glycerine/jeaten-go-arrayof-structof,rdp/rogerpack2005-golang,d0f/go-zh,webfd/go-zh,sanjosh/sanjos100-tipc