Expand tilde on Windows as well (fixes #289)

cmd/syncthing/main.go

@@ -695,6 +695,7 @@ func expandTilde(p string) string {
 		return getHomeDir()
 	}
 
+	p = filepath.FromSlash(p)
 	if !strings.HasPrefix(p, fmt.Sprintf("~%c", os.PathSeparator)) {
 		return p
 	}