* src/eval-apply.c (expand_variable_): Process internal definitions
as local variables; ensure all free variables are bound (creating
bindings if necessary).
(eval_apply): When evaluating a pair with a binding in its car,
evaluate the binding before dispatching; when evaluating a binding,
raise an error if the location does not have a value.
* src/mes.c (mes_environment): Bind special symbols to themselves.
* mes/module/mes/boot-0.scm (defined?): Make sure the variable
actually has a value.
* mes/module/mes/boot-00.scm (defined?): Likewise.
* mes/module/mes/boot-01.scm (defined?): Likewise.
* mes/module/mes/boot-02.scm (defined?): Likewise.
* mes/module/mes/boot-03.scm (defined?): Likewise.
* scaffold/boot/60-let-syntax-expanded.scm (defined?): Likewise.