initargs and change-class

[Gregor J. Kiczales <gregor@parc.xerox.com>]

It appears that we never made the change to have change-class and
update-instance-for-redefined-class accept initialization arguments.
We should do this, a number of people have asked for it, it is
consistent, simple, and provides an elegant way to pass information
about why the class is being changed.

In fact, it seems (to me at least) that this is just something we forgot
to do before rather than a real decision we made not to do it.