Priority Queue class prototypes.
Priority queues maintain collections of objects arranged for fast access to the least element.
Several prototype implementations of priority queues are supported. XPPQs implement 2-ary heaps via XPlexes. The simple-splay mechanism for priority queue functions is loosely based on the one used by D. Jones in the C splay tree functions available from volume 14 of the uunet.uu.net archives. Storage for heap elements is managed via an internal freelist technique. The constructor allows an initial capacity estimate for freelist space.