Add self-contained gometalinter build tooling.

tools/vendor/github.com/mvdan/lint/LICENSE

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+Copyright (c) 2017, Daniel Martí. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+   * Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+   * Redistributions in binary form must reproduce the above
+copyright notice, this list of conditions and the following disclaimer
+in the documentation and/or other materials provided with the
+distribution.
+   * Neither the name of the copyright holder nor the names of its
+contributors may be used to endorse or promote products derived from
+this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

tools/vendor/github.com/mvdan/lint/README.md

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+# lint
+
+[![GoDoc](https://godoc.org/github.com/mvdan/lint?status.svg)](https://godoc.org/github.com/mvdan/lint)
+[![Build Status](https://travis-ci.org/mvdan/lint.svg?branch=master)](https://travis-ci.org/mvdan/lint)
+
+Work in progress. Its API might change before the 1.0 release.
+
+This package intends to define simple interfaces that Go code checkers
+can implement. This would simplify calling them from Go code, as well as
+running multiple linters while sharing initial loading work.
+
+### metalint
+
+	go get -u github.com/mvdan/lint/cmd/metalint
+
+The start of a linter that runs many linters leveraging the common
+interface. Not stable yet.
+
+Linters included:
+
+* [unparam](https://github.com/mvdan/unparam)
+* [interfacer](https://github.com/mvdan/interfacer)
+
+### Related projects
+
+* [golinters](https://github.com/thomasheller/golinters) - Report on
+  linter support

tools/vendor/github.com/mvdan/lint/lint.go

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+// Copyright (c) 2017, Daniel Martí <mvdan@mvdan.cc>
+// See LICENSE for licensing information
+
+// Package lint defines common interfaces for Go code checkers.
+package lint
+
+import (
+	"go/token"
+
+	"golang.org/x/tools/go/loader"
+	"golang.org/x/tools/go/ssa"
+)
+
+// A Checker points out issues in a program.
+type Checker interface {
+	Program(*loader.Program)
+	Check() ([]Issue, error)
+}
+
+type WithSSA interface {
+	ProgramSSA(*ssa.Program)
+}
+
+// Issue represents an issue somewhere in a source code file.
+type Issue interface {
+	Pos() token.Pos
+	Message() string
+}