[release-branch.go1.11-security] cmd/go: reject 'get' of paths containing leading dots or unsupported characters
On some platforms, directories beginning with dot are treated as
hidden files, and filenames containing unusual characters can be
confusing for users to manipulate (and delete).
Change-Id: Ia1f5a65b9cff4eeb51cc4dba3ff7c7afabc343f2
Reviewed-on: https://team-review.git.corp.google.com/c/368442 Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>