cmd/vendor: add x/tools/go/analysis/cmd/vet-lite + deps

This change adds the vet-lite command (the future cmd/vet) and all its
dependencies from x/tools, but not its tests and their dependencies.
It was created with these commands:

  $ (cd $GOPATH/src/golang.org/x/tools && git checkout c76e1ad)
  $ cd GOROOT/src/cmd
  $ govendor add $(go list -deps golang.org/x/tools/go/analysis/cmd/vet-lite | grep golang.org/x/tools)
  $ rm -fr $(find vendor/golang.org/x/tools/ -name testdata)
  $ rm $(find vendor/golang.org/x/tools/ -name \*_test.go)

I feel sure I am holding govendor wrong. Please advise.

A followup CL will make cmd/vet behave like vet-lite, initially just
for users that opt in, and soon after for all users, at which point
cmd/vet will be replaced in its entirety by a copy of vet-lite's small
main.go.

In the meantime, anyone can try the new tool using these commands:

 $ go build cmd/vendor/golang.org/x/tools/go/analysis/cmd/vet-lite
 $ export GOVETTOOL=$(which vet-lite)
 $ go vet your/project/...

Change-Id: Iea168111a32ce62f82f9fb706385ca0f368bc869
Reviewed-on: https://go-review.googlesource.com/c/147444


Reviewed-by: Russ Cox <rsc@golang.org>