Previously they only showed for My Library by default, which I suspect
meant that most people didn't know you could get them for other
libraries...
This hides "Duplicate Items" and "Unfiled Items" from the context menu
when they're active, which may or may not be desirable (but we don't
show, say, "Trash" in the context menu).
Also tweaks selection behavior after hide to select next appropriate row
instead of the parent library.