Undo redo (again) - deleted/undone nodes can't be reopened

[jimfinnis]

• Load up the 671483 example.
• Delete a bunch of things, including the gradient.
• Undo that, and try to reopen the gradient. You can't.

[jimfinnis]

Perhaps it's this:

• create node, open tab, tab is added to internal tab system
• delete node, the tab is deleted
• undo delete, can't recreate tab because it thinks there already is one??

Looks like that's it - openTab scans the tabs (a bit inefficient, that) and finds a tab is still there in node.tabs.

So how does undo work when it comes to restoring deleted nodes? Or rather, should delete remove a node's tabs? That won't work because the mark is done before the remove; we're still recording that the node has tabs.

Hm.. the bug is earlier; I don't think that deleting a node (which closes its tabs) removes the tab from mainwindow's dict. It seems that closing a tab when a node is deleted isn't done using the normal method (calling closeTab on the window).

[jimfinnis]

Fixed in ae001d84ec9dbb476479f2331b1cdba928ddadb7