don't change smooth nodes to corner/cusp when adjacent nodes are deleted

Migrated from: https://bugs.launchpad.net/inkscape/+bug/257771

Steps to reproduce:

• draw a path with smooth curves in it, using at least 6 smooth nodes
• delete one of the smooth nodes in the middle of the path

What happened?

Notice that 2 of the previously smooth nodes in the smoothly curved path have been changed to corner/cusp nodes.

What should have happened?

I think they should remain smooth, as the user has previously defined them. I don't understand the purpose for the node type being changed. And if I wanted them cusp/corner, I would have made them that way.

If there is some reason for the changing node types, perhaps this could be an optional feature?

The last status info from that report was:

Changed in inkscape: importance: Undecided → Wishlist status: New → Confirmed

Thank you very much.