mini_object_replace

Atomically modifies a pointer to point to a new mini-object.

The reference count of olddata is decreased and the reference count of newdata is increased.

Either newdata and the value pointed to by olddata may be null.

Parameters:

olddata	pointer to a pointer to a mini-object to be replaced
newdata	pointer to new mini-object

Returns:

true if newdata was different from olddata