YTreeitems are inserted twice in YTree

[anaselli]

Using the code example used to show the evidence of issue #54, the application presents the items inserted twice into the tree.
That happens in ncurses only, and using tree->startMultipleChanges(); .... tree->doneMultipleChanges(); code block. Even if in that example we could avoid such a multiple changes, this issue happens also when removing old items and then adding the new ones, e.g. in a common condition at run-time.
I haven't found any workarounds for this so it's blocking for me since it breaks the normal behaviour.