Update dependencies, enable pruning for vendor/

So, `dep` got an nice new feature to remove tests and non-go files from
`vendor/`, and this brings the size of the vendor directory from ~300MiB
down to ~20MiB. We don that now.

vendor/github.com/pkg/sftp/request-server.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding"
 	"io"
+	"os"
 	"path"
 	"path/filepath"
 	"strconv"
@@ -128,9 +129,18 @@ func (rs *RequestServer) Serve() error {
 
 		pkt, err = makePacket(rxPacket{fxp(pktType), pktBytes})
 		if err != nil {
-			debug("makePacket err: %v", err)
-			rs.conn.Close() // shuts down recvPacket
-			break
+			switch errors.Cause(err) {
+			case errUnknownExtendedPacket:
+				if err := rs.serverConn.sendError(pkt, ErrSshFxOpUnsupported); err != nil {
+					debug("failed to send err packet: %v", err)
+					rs.conn.Close() // shuts down recvPacket
+					break
+				}
+			default:
+				debug("makePacket err: %v", err)
+				rs.conn.Close() // shuts down recvPacket
+				break
+			}
 		}
 
 		pktChan <- pkt
@@ -164,8 +174,16 @@ func (rs *RequestServer) packetWorker(
 			rpkt = cleanPacketPath(pkt)
 		case *sshFxpOpendirPacket:
 			request := requestFromPacket(ctx, pkt)
-			handle := rs.nextRequest(request)
-			rpkt = sshFxpHandlePacket{pkt.id(), handle}
+			rpkt = request.call(rs.Handlers, pkt)
+			if stat, ok := rpkt.(*sshFxpStatResponse); ok {
+				if stat.info.IsDir() {
+					handle := rs.nextRequest(request)
+					rpkt = sshFxpHandlePacket{pkt.id(), handle}
+				} else {
+					rpkt = statusFromError(pkt, &os.PathError{
+						Path: request.Filepath, Err: syscall.ENOTDIR})
+				}
+			}
 		case *sshFxpOpenPacket:
 			request := requestFromPacket(ctx, pkt)
 			handle := rs.nextRequest(request)