title:  Tagging and Gluing
desc: tag glue trouble

Now we get some commands to actually do something.  What
we want the user to be able to do is first `tag' a selected side,
then later select one or more sides, and finally 
give another command `glue to tagged', which will move the
selected sides so that they are coplanar with the tagged one.
So we will actually need two (eventually three) commands
in all.

