sync parse.y changes from base; ok naddy@

original from naddy@:
> Don't declare variables as "unsigned char *" that are passed to
> functions that take "char *" arguments.  Where such chars are
> assigned to int or passed to ctype functions, explicitly cast them
> to unsigned char.
>
> For OpenBSD's clang, -Wpointer-sign has been disabled by default,
> but when the parse.y code was built elsewhere, the compiler would
> complain.
>
> With help from millert@
> ok benno@ deraadt@