lsf: implement 'i' format for showing object ID - fixes #1476

fs/operations/operations.go

@@ -1420,6 +1420,16 @@ func (l *ListFormat) AddHash(ht hash.Type) {
 	})
 }
 
+// AddID adds file's ID to the output if known
+func (l *ListFormat) AddID() {
+	l.AppendOutput(func() string {
+		if do, ok := l.entry.(fs.IDer); ok {
+			return do.ID()
+		}
+		return ""
+	})
+}
+
 // AppendOutput adds string generated by specific function to printed output
 func (l *ListFormat) AppendOutput(functionToAppend func() string) {
 	if len(l.output) > 0 {