dropbox: add missing dbhashsum command

This was missed from 6381959850

cmd/dbhashsum/dbhashsum.go

@@ -0,0 +1,31 @@
+package dbhashsum
+
+import (
+	"os"
+
+	"github.com/ncw/rclone/cmd"
+	"github.com/ncw/rclone/fs"
+	"github.com/spf13/cobra"
+)
+
+func init() {
+	cmd.Root.AddCommand(commandDefintion)
+}
+
+var commandDefintion = &cobra.Command{
+	Use:   "dbhashsum remote:path",
+	Short: `Produces a Dropbbox hash file for all the objects in the path.`,
+	Long: `
+Produces a Dropbox hash file for all the objects in the path.  The
+hashes are calculated according to [Dropbox content hash
+rules](https://www.dropbox.com/developers/reference/content-hash).
+The output is in the same format as md5sum and sha1sum.
+`,
+	Run: func(command *cobra.Command, args []string) {
+		cmd.CheckArgs(1, 1, command, args)
+		fsrc := cmd.NewFsSrc(args)
+		cmd.Run(false, false, command, func() error {
+			return fs.DropboxHashSum(fsrc, os.Stdout)
+		})
+	},
+}