Follow-up of #1117882: Update hook_features_pipe_alter() with D7 variables

Hi,

There still is node_preview missing from the updated list of variables to take into account ;-)

What about taking every variable ending by $node_type, since it seems to become a naming pattern for more and more modules ? I suppose it has already been well-thought and there are good reasons for not doing it.
Anyway, I provide the patch for the missing variable.