all selects are turned into itemsets

[MartijnR]

Both old-style cascading selects (this may be a feature and not a bug) as well as normal selects are turned into itemsets. Maybe this is related to using cascading_select anywhere in the form.

See this form: https://formhub.org/martijnr/forms/bench7

This issue looks like #71 but this form doesn't contain a choice_filter.