[Mimedefang] Part’s parent content-type

[Amit Gupta]

Thank you Dianne! This is going to sound silly, but what I'm looking
for is a function like

$parent_part = get_parent ($top_entity, $part);

So given the top level entity and a specific part, the function will
return the MIME::Entity for the parent of $part.  I'm struggling with
getting the recursion on this.  Any tips on a simple way to do this?