altos/lisp: Make sure memmove only happens once per object. Other GC fixes

altos/lisp: Make sure memmove only happens once per object. Other GC fixes

The memmove may be overlapping, so make sure it happens only once by
just checking whether move_size has been set, rather than looking at
ao_lisp_moving; that doesn't get set when moving a noted cons as that
still needs to be walked at a later time.

Fix up the various looping move functions to all use the same
pattern. Atom was busted.

Signed-off-by: Keith Packard <keithp@keithp.com>