find.go
func (f *FindFilter) IfMode(fn func(os.FileMode) bool) *FindFilter {
	f.ifmode = fn
	return f
}
func (f *FindFilter) IfMode(fn func(os.FileMode) bool) *FindFilter {
	f.ifmode = fn
	return f
}
// IfMode adjusts f so it only matches nodes for which fn(mode) returns true.