copy_node procedure

i would like to be able to copy a node and all of it's structure underneath to under another node. so like move, but a copy. is this something i can contract you to add? if not, i'll add it and contribute it if it is helpful.

[werc]

For now, I would try to select node and leaves - subtree (depth of the leaf is there too) and insert them in loop one by one, under parent.