os: fix FileInfo.Name returned by Stat

Fixes #1645.

R=rsc
CC=golang-dev
https://golang.org/cl/4321045

src/pkg/os/file_unix.go

@@ -102,3 +102,21 @@ func Truncate(name string, size int64) Error {
 	}
 	return nil
 }
+
+// basename removes trailing slashes and the leading directory name from path name
+func basename(name string) string {
+	i := len(name) - 1
+	// Remove trailing slashes
+	for ; i > 0 && name[i] == '/'; i-- {
+		name = name[:i]
+	}
+	// Remove leading directory name
+	for i--; i >= 0; i-- {
+		if name[i] == '/' {
+			name = name[i+1:]
+			break
+		}
+	}
+
+	return name
+}