Make "findParent" work on Windows properly

Fixes #31

memmap.go

diff --git a/memmap.go b/memmap.go
index caa0cf3..06799c6 100644
--- a/memmap.go
+++ b/memmap.go
@@ -18,7 +18,6 @@
 	"fmt"
 	"log"
 	"os"
-	"path"
 	"path/filepath"
 	"sort"
 	"strings"
@@ -118,8 +117,8 @@
 }
 
 func (m *MemMapFs) findParent(f File) File {
-	pdir, _ := path.Split(f.Name())
-	pdir = path.Clean(pdir)
+	pdir, _ := filepath.Split(f.Name())
+	pdir = filepath.Clean(pdir)
 	pfile, err := m.lockfreeOpen(pdir)
 	if err != nil {
 		return nil
@@ -133,7 +132,7 @@
 	}
 	parent := m.findParent(f)
 	if parent == nil {
-		pdir := filepath.Dir(path.Clean(f.Name()))
+		pdir := filepath.Dir(filepath.Clean(f.Name()))
 		err := m.lockfreeMkdir(pdir, 0777)
 		if err != nil {
 			//log.Println("Mkdir error:", err)