Setting a property path like "article.tags" will now automatically try to
favor addTag() and removeTag() over setTags(), if found. If you want to
set up a property path with an irregular singular that is not detected,
you can use "|" to separate the plural from the singular form in the
path: "article.genera|genus".
Another consequence of this commit is that the MergeCollectionListener has
been simplified a lot. Forms returning an array or a collection will
always result in adders/removers being called now without having to add
this listener.
