ctree/clist row selections

[Tim Janik <timj gtk org>]

hi lars,

i need to be able to intercept row/node selections in clists/ctrees.
currently::select_row and ::unselect_row are GTK_RUN_FIRST signals
and can't be intercepted. after browsing some clist code, i figured
that simply making them GTK_RUN_LAST would actually interfere with
implicit assumptions the code makes, i.e. it relies on ::unselect_row
to clear up clist->selection, and probably else stuff.
since interception is not currently possible with clist, can we
either provide something like a ::check_select_row signal, or simply
a possibility to mark certain rows/nodes unselectable?

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ciaoTJ