fusefrontend: handle Readlink directly
fusefrontend: handle Readlink directly

Calling into go-fuse's loopbackFileSystem does not add
any value here.

rfjakob/gocryptfs,davesteele/gocryptfs,rfjakob/gocryptfs,rfjakob/gocryptfs,davesteele/gocryptfs,rfjakob/gocryptfs,davesteele/gocryptfs