list objects: obey encoding-type

Before this change we unconditionally set encoding-type=url which was
confusing some clients.

After this change we do URL encoding only if it was requested.

NB This will require the backend to not URL encode keys which rclone
was doing before.

Fixes #4

gofakes3.go

@@ -235,6 +235,11 @@ func (g *GoFakeS3) listBucket(bucketName string, w http.ResponseWriter, r *http.
 	}
 
 	isVersion2 := q.Get("list-type") == "2"
+	encodingType := q.Get("encoding-type")
+	useUrlEncoding := encodingType == "url"
+	if !useUrlEncoding && encodingType != "" {
+		return ErrInvalidArgument
+	}
 
 	g.log.Print(LogInfo, "bucketname:", bucketName, "prefix:", prefix, "page:", fmt.Sprintf("%+v", page))
 
@@ -266,9 +271,19 @@ func (g *GoFakeS3) listBucket(bucketName string, w http.ResponseWriter, r *http.
 		Contents:       objects.Contents,
 		IsTruncated:    objects.IsTruncated,
 		Delimiter:      prefix.Delimiter,
-		Prefix:         URLEncode(prefix.Prefix),
+		Prefix:         prefix.Prefix,
 		MaxKeys:        page.MaxKeys,
-		EncodingType:   "url",
+		EncodingType:   encodingType,
+	}
+	if useUrlEncoding {
+		base.Prefix = URLEncode(base.Prefix)
+		for i := range base.CommonPrefixes {
+			prefix := &base.CommonPrefixes[i]
+			prefix.Prefix = URLEncode(prefix.Prefix)
+		}
+		for _, content := range base.Contents {
+			content.Key = URLEncode(content.Key)
+		}
 	}
 
 	if !isVersion2 {