Nuke away old nodeCopyNode(), much better to use new BKE_node_copy_ex(),
which behaves as expected for the various optional flags that can be passed.
This also removes the need to handle ID refcounting in calling code
(ugly!) and allows us to remove an even uglier name from our codebase! :D
Note that this fixes three related issues actually, that bug was also
affecting copy/paste of nodes, and 'Separate with copy' operator (the
latter being actually fully wrong, since it was not refcounting
anything, not even node->id pointer...).
c6e3a20ab6