structure references in header files

[VLD/VMB]

The approved way to declare two structs each of which has a
member that is a pointer to the other type of struct, is:

struct a;

struct b {
	struct *a;
	};

struct a {
	struct *b;
	};

Yes, I know it looks unbelievable.  This kludge is present
precisely to handle this kind of problem.