Incompatible change to PROG

[RMS at MIT-AI (Richard M. Stallman)]

Soon PROG will bind all the variables in parallel
instead of sequentially.  This only makes a difference
if you have initializations which depend on other
variables bound by the same PROG.

If you want to bind variables sequentially, use PROG*,
which is presently the same as PROG and will not change.

Old QFASL files will continue to work as before.
The change takes effect only when the program is recompiled.

I plan to create LET* and DO*, which will both do sequential
binding like PROG*, at some time in the future.