* eval.c (SCM_CEVAL): Do more thorough argument checking. This

* eval.c (SCM_CEVAL): Do more thorough argument checking.  This
change makes the evaluator safer at the cost of evaluation speed.
It handles the case when the user has added a non-immediate
improper end of the application form, e.g., `(+ 0 . x)'.
(Earlier only cases like `(+ 0 . 0)' were handled.)  I've tried to
minimize the extra cost as much as possible.  The new code is
enclosed in #ifdef CAUTIOUS regions.  NOTE: This also fixes the
problem with structs planted directly in the code (e.g. by a
macro).  This no longer causes segmentation fault.  (Thanks to
Eric Hanchrow.)

* eval.c, eval.h (scm_eval_args, scm_deval_args): Take one extra
arg `proc' in order to be able to throw errors; New argument
checking code.