expander: relax sys:setq and lisp-1 stringency.

The motivation here is that there are behaviors in the
expander which hinder symbol-macro-based renaming techniques.
For instance (expand '(symacrolet ((x y)) (sys:setq x x)))
throws. The right hand side of the setq is fine, but the left
hand one is a forbidden symbol macro. Yet, we would just like
this to expand to (sys:setq y y). The original idea was that
sys:setq occurs as a result of macro-expansion. Therefore,
if its argument is a symbol macro, something must be wrong; it
didn't get expanded. That reasoning is wrong in the face of
explicit expansion techniques that make multiple expansion
passes. For instance (set a b) can become something like
(sys:setq #:g0005 #:g0007) when the intent that in another round
of renaming these gensyms will be defined as symbol macros
which perform one more renaming.

* eval.c (expand_lisp1_value, expand_lisp1_setq): Macro-expand
the symbol and work with the expanded one. We still keep the
check for a symbol macro; these situations can arise if a
symbol macro cannot expand due to circularity.
(do_expand): When checking sys:setq for a bad symbol or symbol
macro, work with the expanded argument.

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