To remove the const qualifier from a pointer to an object - either

To remove the const qualifier from a pointer to an object - either
because we know it is actually mutable or because we are passing
it to a function that doesn't accept a const object but won't
actually attempt to modify it - simply casting from (const type *)
to (type *) is legal C and clearly expresses the intent.
So get rid of the obfuscating UNCONST macro.
Basic idea discussed with guenther@.