replace "dep" with "go mod"

A simple "go mod init && go mod tidy && go mod vendor" was enough and
mostly seems to have picked the same revisions of the dependencies as
before. Notable exceptions are klog and gogo/protobuf.

vendor/github.com/gogo/protobuf/GOLANG_CONTRIBUTORS

@@ -1,5 +0,0 @@
-The contributors to the Go protobuf repository:
-
-# This source code was written by the Go contributors.
-# The master list of contributors is in the main Go distribution,
-# visible at http://tip.golang.org/CONTRIBUTORS.

vendor/github.com/gogo/protobuf/proto/Makefile

@@ -0,0 +1,43 @@
+# Go support for Protocol Buffers - Google's data interchange format
+#
+# Copyright 2010 The Go Authors.  All rights reserved.
+# https://github.com/golang/protobuf
+#
+# 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 Google Inc. 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.
+
+install:
+	go install
+
+test: install generate-test-pbs
+	go test
+
+
+generate-test-pbs:
+	make install
+	make -C test_proto
+	make -C proto3_proto
+	make

vendor/github.com/gogo/protobuf/proto/extensions.go

@@ -527,6 +527,7 @@ func ExtensionDescs(pb Message) ([]*ExtensionDesc, error) {
 // SetExtension sets the specified extension of pb to the specified value.
 func SetExtension(pb Message, extension *ExtensionDesc, value interface{}) error {
 	if epb, ok := pb.(extensionsBytes); ok {
+		ClearExtension(pb, extension)
 		newb, err := encodeExtension(extension, value)
 		if err != nil {
 			return err

vendor/github.com/gogo/protobuf/proto/extensions_gogo.go

@@ -154,6 +154,10 @@ func EncodeInternalExtension(m extendableProto, data []byte) (n int, err error)
 	return EncodeExtensionMap(m.extensionsWrite(), data)
 }
 
+func EncodeInternalExtensionBackwards(m extendableProto, data []byte) (n int, err error) {
+	return EncodeExtensionMapBackwards(m.extensionsWrite(), data)
+}
+
 func EncodeExtensionMap(m map[int32]Extension, data []byte) (n int, err error) {
 	o := 0
 	for _, e := range m {
@@ -169,6 +173,23 @@ func EncodeExtensionMap(m map[int32]Extension, data []byte) (n int, err error) {
 	return o, nil
 }
 
+func EncodeExtensionMapBackwards(m map[int32]Extension, data []byte) (n int, err error) {
+	o := 0
+	end := len(data)
+	for _, e := range m {
+		if err := e.Encode(); err != nil {
+			return 0, err
+		}
+		n := copy(data[end-len(e.enc):], e.enc)
+		if n != len(e.enc) {
+			return 0, io.ErrShortBuffer
+		}
+		end -= n
+		o += n
+	}
+	return o, nil
+}
+
 func GetRawExtension(m map[int32]Extension, id int32) ([]byte, error) {
 	e := m[id]
 	if err := e.Encode(); err != nil {