cmd/guru: emacs: support running on nameless buffers
cmd/guru: emacs: support running on nameless buffers

By using guru's -modified flag and making up a file name, we can run
guru on a buffer that has no file attached to it. This feature will only
be useful for queries that operate on single files, as otherwise our made
up name could cause conflicts.

This will be useful for the "what" query and features using it.

Change-Id: I3d199bc0548245d59ba7b492f57beb9422d7f43d
Reviewed-on: https://go-review.googlesource.com/20431
Reviewed-by: Alan Donovan <7069e9552f9d110b0a0f326b96f22f63fb99dfc1@google.com>

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