null begin forms

[Chris Haynes <chaynes@iuvax.cs.indiana.edu>]

>From Will's minutes:

    F.  Nested begin expressions containing DEFINE forms will be flattened and
    treated as consecutive DEFINE forms, both at top level and at the head of
    lambda bodies.  Macros will be permitted to expand into definitions and
    BEGIN forms containing definitions.

Does this mean that `(begin)' must be, may be, or may not be, allowed?
It would be very nice, say for debugging statement macros that may not
want to generate anything.  That is, I wish a null begin would compile
nothing if it appeared in any but the last place within another
(implicit or explicit) begin.

-- Chris Haynes