Added (copy) routine

[fowler]

I put a copy routine in Geomview (specifically, drawer.c) that lets
you make an exact copy of an object / camera including modelling
transform, appearance, etc.  Syntax is 
(copy [id of thing to copy] [name for new thing])
I found that before I always ended up writing out temporary files and
then reading them in and copying the transforms etc manually.
-Celeste

PS: This necessitated a very minor change to ApCopy which now returns
NULL if both src and dst are NULL (as opposed to core dumping).