Indirecting foreign objects for libffi

The generic function translate-into-foreign-memory has been slightly
repurposed and expanded to provide indirection of enums and pointers.
The function translate-objects and generic function
expand-to-foreign-dyn have a new argument, 'indirect, that when set,
expand to with-foreign-object and translate-into-foreign-memory
instead of translate-to-foreign, unwind-protect, and
free-translated-object.  This insures that all arguments to functions
passed to libffi are indirected one level, as is required.