Add new NOT_SET macro to call after NOT_NULL for functions that call set*() functions.
Right now for example, getting a new config descriptor re-using an old ConfigDescriptor object just overwrites the old pointer, without freeing it or telling the user, resulting in a memory leak.
This way, the user gets notified when he's re-using an object that he hasn't cleaned up yet, and he can react and call the appropriate free/cleanup function.