all: Become a Go module (fixes #5148) (#5384)

* go mod init; rm -rf vendor

* tweak proto files and generation

* go mod vendor

* clean up build.go

* protobuf literals in tests

* downgrade gogo/protobuf

vendor/github.com/d4l3k/messagediff/README.md

@@ -0,0 +1,90 @@
+# messagediff [![Build Status](https://travis-ci.org/d4l3k/messagediff.svg?branch=master)](https://travis-ci.org/d4l3k/messagediff) [![Coverage Status](https://coveralls.io/repos/github/d4l3k/messagediff/badge.svg?branch=master)](https://coveralls.io/github/d4l3k/messagediff?branch=master) [![GoDoc](https://godoc.org/github.com/d4l3k/messagediff?status.svg)](https://godoc.org/github.com/d4l3k/messagediff)
+
+A library for doing diffs of arbitrary Golang structs.
+
+If the unsafe package is available messagediff will diff unexported fields in
+addition to exported fields. This is primarily used for testing purposes as it
+allows for providing informative error messages.
+
+Optionally, fields in structs can be tagged as `testdiff:"ignore"` to make
+messagediff skip it when doing the comparison.
+
+
+## Example Usage
+In a normal file:
+```go
+package main
+
+import "gopkg.in/d4l3k/messagediff.v1"
+
+type someStruct struct {
+    A, b int
+    C []int
+}
+
+func main() {
+    a := someStruct{1, 2, []int{1}}
+    b := someStruct{1, 3, []int{1, 2}}
+    diff, equal := messagediff.PrettyDiff(a, b)
+    /*
+        diff =
+        `added: .C[1] = 2
+        modified: .b = 3`
+
+        equal = false
+    */
+}
+
+```
+In a test:
+```go
+import "gopkg.in/d4l3k/messagediff.v1"
+
+...
+
+type someStruct struct {
+    A, b int
+    C []int
+}
+
+func TestSomething(t *testing.T) {
+    want := someStruct{1, 2, []int{1}}
+    got := someStruct{1, 3, []int{1, 2}}
+    if diff, equal := messagediff.PrettyDiff(want, got); !equal {
+        t.Errorf("Something() = %#v\n%s", got, diff)
+    }
+}
+```
+To ignore a field in a struct, just annotate it with testdiff:"ignore" like
+this:
+```go
+package main
+
+import "gopkg.in/d4l3k/messagediff.v1"
+
+type someStruct struct {
+    A int
+    B int `testdiff:"ignore"`
+}
+
+func main() {
+    a := someStruct{1, 2}
+    b := someStruct{1, 3}
+    diff, equal := messagediff.PrettyDiff(a, b)
+    /*
+        equal = true
+        diff = ""
+    */
+}
+```
+
+See the `DeepDiff` function for using the diff results programmatically.
+
+## License
+Copyright (c) 2015 [Tristan Rice](https://fn.lc) <rice@fn.lc>
+
+messagediff is licensed under the MIT license. See the LICENSE file for more information.
+
+bypass.go and bypasssafe.go are borrowed from
+[go-spew](https://github.com/davecgh/go-spew) and have a seperate copyright
+notice.