cmd/gomtree/main.go: Handle Extra and Missing cases

The BSD format needed a slight tweak to handle mtree.Extra
and mtree.Missing cases.  It currently only handled the 'Modified'
cases and therefore was not showing missing or extra files during
validation.

cmd/gomtree/main.go

@@ -291,6 +291,10 @@ var formats = map[string]func([]mtree.InodeDelta) string{
 		for _, delta := range d {
 			if delta.Type() == mtree.Modified {
 				fmt.Fprintln(&buffer, delta)
+			} else if delta.Type() == mtree.Missing {
+				fmt.Fprintln(&buffer, delta)
+			} else if delta.Type() == mtree.Extra {
+				fmt.Fprintln(&buffer, delta)
 			}
 		}
 		return buffer.String()