Separate the "is asshole off limits?" logic from the helper logic

Creature.assholeOffLimits() now takes no parameters and always returns a boolean; BaseContent.assholeOffLimits() takes parameters and returns one of them.
Fix a likely bug in plantgirl.as

Why isn't this a compiler error?
Use Heckel's oral scene for loss with no-anal players
Hide anal Heckel option for no-anal players

Also reorganizes Heckel scene's coding to reduce redundancy.