cmd/guru: emacs: report an error when the guru command fails
cmd/guru: emacs: report an error when the guru command fails

Don't just display the output buffer or, worse, parse it as JSON.

Change-Id: I1125ff235a5073b07f45f587ef8844b8a12f05ac
Reviewed-on: https://go-review.googlesource.com/19508
Reviewed-by: Michael Matloob <4562438b12c14e81a47550acde616ff328a909f8@golang.org>

emacsmirror/go-mode,dominikh/go-mode.el