cmd/guru: implements: if selected expr is a value, use its type

...as the basis of the query, instead of reporting an error.

+ test

Change-Id: Ie5defa98cd8dfc8e200e296c2aa02c88893cf9ac
Reviewed-on: https://go-review.googlesource.com/22117
Reviewed-by: Michael Matloob <matloob@golang.org>
3 files changed