RelatedItems: do not show not selectable items

[jensens]

If one passes the RelatedItems pattern a list of 'selectableTypes', it does not make sense to show non-folderish types not in this list.

[davisagli]

It looks like this was implemented sometime: there is currently code to filter out non-selectable items.

However, it has a bug. When browsing rather than searching, the pattern asks the server for all types, and then filters them on the client side. This is so that it can include folderish types in the results. But, if there are multiple pages of results and all of the results in the first page are not selectable, then the pattern shows a "no results" message even if there are valid results on later pages.

I suspect that the right solution is to configure the pattern with a list of folderish types, and make it ask the server for the union of folderish and selectable types when browsing, so that this filtering happens on the server side rather than the client side.

[thet]

The reasoning was for the behavior was as @davisagli described. I wasn't aware of the bug.
Doing the filtering server side (using the is_folderish index) sounds good.