Fix parent not present on Windows

This will (in some cases?) `syscall.ENOTDIR`.

Fixes #86

copyOnWriteFs.go

diff --git a/copyOnWriteFs.go b/copyOnWriteFs.go
index fa0c936..ed692ae 100644
--- a/copyOnWriteFs.go
+++ b/copyOnWriteFs.go
@@ -32,7 +32,7 @@
 	_, err := u.base.Stat(name)
 	if err != nil {
 		if oerr, ok := err.(*os.PathError); ok {
-			if oerr.Err == os.ErrNotExist || oerr.Err == syscall.ENOENT {
+			if oerr.Err == os.ErrNotExist || oerr.Err == syscall.ENOENT || oerr.Err == syscall.ENOTDIR {
 				return false, nil
 			}
 		}
@@ -80,7 +80,7 @@
 		if e, ok := err.(*os.PathError); ok {
 			err = e.Err
 		}
-		if err == syscall.ENOENT {
+		if err == syscall.ENOENT || err == syscall.ENOTDIR {
 			return u.base.Stat(name)
 		}
 		return nil, origErr