Notify GtkTreeView if a node stops being a parent.
GtkTreeView requires the row-has-child-toggled signal to be emitted in
this situation, so do it from ItemDeleted handler.
Curiously, it handles adding the first child automatically. That's good,
because detecting this situation when adding the first child wouldn't be
trivial and so not having to do it is a plus. (Emitting it on every node
addition doesn't sound like a terribly bright idea.)
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68915
c3d73ce0-8a6f-49c7-b76d-
6d57e0e08775