Fix location of config/ manifest link, and add test.

Change-Id: I9e0483b4d63c3a0754fc92ad7a499f697414ffae

fs/gitilesfs_test.go

diff --git a/fs/gitilesfs_test.go b/fs/gitilesfs_test.go
index eaddca9..dec33e6 100644
--- a/fs/gitilesfs_test.go
+++ b/fs/gitilesfs_test.go
@@ -706,10 +706,14 @@
 
 	if got, err := os.Readlink(configName); err != nil {
 		t.Fatalf("Readlink(%s): %", configName, err)
-	} else if want := "../ws/manifest.xml"; got != want {
+	} else if want := "../ws/.slothfs/manifest.xml"; got != want {
 		t.Errorf("got link %s, want %s", got, want)
 	}
 
+	if _, err := manifest.ParseFile(configName); err != nil {
+		t.Fatalf("ParseFile(%s): %v", configName, err)
+	}
+
 	fn := filepath.Join(wsDir, "build", "kati", "AUTHORS")
 	if fi, err := os.Lstat(fn); err != nil {
 		t.Fatalf("Lstat(%s): %v", fn, err)

fs/multifs.go

diff --git a/fs/multifs.go b/fs/multifs.go
index 5711e22..e67a4fd 100644
--- a/fs/multifs.go
+++ b/fs/multifs.go
@@ -135,7 +135,7 @@
 	config := c.Inode().NewChild(name, false, &configEntryNode{
 		Node: nodefs.NewDefaultNode(),
 		// This is sneaky, but it appears to work.
-		link: []byte(filepath.Join("..", name, "manifest.xml")),
+		link: []byte(filepath.Join("..", name, ".slothfs", "manifest.xml")),
 	})
 
 	if err := fs.(*manifestFSRoot).onMount(c.root.fsConn); err != nil {