Be more verbose in panic message.

fuse/pathfilesystem.go

@@ -256,7 +256,9 @@ func (self *PathFileSystemConnector) Destroy(h *InHeader, input *InitIn) {
 func (self *PathFileSystemConnector) Lookup(header *InHeader, name string) (out *EntryOut, status Status) {
 	parent, ok := self.inodePathMapByInode[header.NodeId]
 	if !ok {
-		panic("Parent inode unknown.")
+		msg := fmt.Sprintf("node %v, header %v, name %v",
+			header.NodeId, header, name)
+		panic("Parent inode unknown. " + msg)
 	}
 
 	// TODO - fuse.c has special case code for name == "." and