Update go dep (#1560)

This fix updates go dep with `dep ensure --update` as well as the following:
- Removed github.com/ugorji/go restriction in Gopkg.toml (fixes  #1557)
- Added github.com/flynn/go-shlex in Makefile (neede by Caddy, maybe removed later)

This fix fixes #1557

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

vendor/github.com/golang/protobuf/proto/discard.go

@@ -0,0 +1,151 @@
+// Go support for Protocol Buffers - Google's data interchange format
+//
+// Copyright 2017 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.
+
+package proto
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+)
+
+// DiscardUnknown recursively discards all unknown fields from this message
+// and all embedded messages.
+//
+// When unmarshaling a message with unrecognized fields, the tags and values
+// of such fields are preserved in the Message. This allows a later call to
+// marshal to be able to produce a message that continues to have those
+// unrecognized fields. To avoid this, DiscardUnknown is used to
+// explicitly clear the unknown fields after unmarshaling.
+//
+// For proto2 messages, the unknown fields of message extensions are only
+// discarded from messages that have been accessed via GetExtension.
+func DiscardUnknown(m Message) {
+	discardLegacy(m)
+}
+
+func discardLegacy(m Message) {
+	v := reflect.ValueOf(m)
+	if v.Kind() != reflect.Ptr || v.IsNil() {
+		return
+	}
+	v = v.Elem()
+	if v.Kind() != reflect.Struct {
+		return
+	}
+	t := v.Type()
+
+	for i := 0; i < v.NumField(); i++ {
+		f := t.Field(i)
+		if strings.HasPrefix(f.Name, "XXX_") {
+			continue
+		}
+		vf := v.Field(i)
+		tf := f.Type
+
+		// Unwrap tf to get its most basic type.
+		var isPointer, isSlice bool
+		if tf.Kind() == reflect.Slice && tf.Elem().Kind() != reflect.Uint8 {
+			isSlice = true
+			tf = tf.Elem()
+		}
+		if tf.Kind() == reflect.Ptr {
+			isPointer = true
+			tf = tf.Elem()
+		}
+		if isPointer && isSlice && tf.Kind() != reflect.Struct {
+			panic(fmt.Sprintf("%T.%s cannot be a slice of pointers to primitive types", m, f.Name))
+		}
+
+		switch tf.Kind() {
+		case reflect.Struct:
+			switch {
+			case !isPointer:
+				panic(fmt.Sprintf("%T.%s cannot be a direct struct value", m, f.Name))
+			case isSlice: // E.g., []*pb.T
+				for j := 0; j < vf.Len(); j++ {
+					discardLegacy(vf.Index(j).Interface().(Message))
+				}
+			default: // E.g., *pb.T
+				discardLegacy(vf.Interface().(Message))
+			}
+		case reflect.Map:
+			switch {
+			case isPointer || isSlice:
+				panic(fmt.Sprintf("%T.%s cannot be a pointer to a map or a slice of map values", m, f.Name))
+			default: // E.g., map[K]V
+				tv := vf.Type().Elem()
+				if tv.Kind() == reflect.Ptr && tv.Implements(protoMessageType) { // Proto struct (e.g., *T)
+					for _, key := range vf.MapKeys() {
+						val := vf.MapIndex(key)
+						discardLegacy(val.Interface().(Message))
+					}
+				}
+			}
+		case reflect.Interface:
+			// Must be oneof field.
+			switch {
+			case isPointer || isSlice:
+				panic(fmt.Sprintf("%T.%s cannot be a pointer to a interface or a slice of interface values", m, f.Name))
+			default: // E.g., test_proto.isCommunique_Union interface
+				if !vf.IsNil() && f.Tag.Get("protobuf_oneof") != "" {
+					vf = vf.Elem() // E.g., *test_proto.Communique_Msg
+					if !vf.IsNil() {
+						vf = vf.Elem()   // E.g., test_proto.Communique_Msg
+						vf = vf.Field(0) // E.g., Proto struct (e.g., *T) or primitive value
+						if vf.Kind() == reflect.Ptr {
+							discardLegacy(vf.Interface().(Message))
+						}
+					}
+				}
+			}
+		}
+	}
+
+	if vf := v.FieldByName("XXX_unrecognized"); vf.IsValid() {
+		if vf.Type() != reflect.TypeOf([]byte{}) {
+			panic("expected XXX_unrecognized to be of type []byte")
+		}
+		vf.Set(reflect.ValueOf([]byte(nil)))
+	}
+
+	// For proto2 messages, only discard unknown fields in message extensions
+	// that have been accessed via GetExtension.
+	if em, ok := extendable(m); ok {
+		// Ignore lock since discardLegacy is not concurrency safe.
+		emm, _ := em.extensionsRead()
+		for _, mx := range emm {
+			if m, ok := mx.value.(Message); ok {
+				discardLegacy(m)
+			}
+		}
+	}
+}