reverse: initialize the longname cache only when reverse mode is used

Gets rid of the idling longnameCacheCleaner thread in "normal" mode.

internal/fusefrontend_reverse/reverse_longnames.go

@@ -30,7 +30,10 @@ func longnameCacheCleaner() {
 	}
 }
 
-func init() {
+func initLongnameCache() {
+	if longnameParentCache != nil {
+		return
+	}
 	longnameParentCache = map[string]string{}
 	go longnameCacheCleaner()
 }

internal/fusefrontend_reverse/rfs.go

@@ -47,6 +47,8 @@ var _ pathfs.FileSystem = &reverseFS{}
 
 // NewFS returns an encrypted FUSE overlay filesystem
 func NewFS(args fusefrontend.Args) pathfs.FileSystem {
+	initLongnameCache()
+
 	cryptoCore := cryptocore.New(args.Masterkey, args.CryptoBackend, contentenc.DefaultIVBits)
 	contentEnc := contentenc.New(cryptoCore, contentenc.DefaultBS)
 	nameTransform := nametransform.New(cryptoCore, args.LongNames)