Add Priority Queue

[thomasm]

TPIE should have it's own priority queue. Lars Hvam Petersen has developed a couple of priority queues for his masters thesis and has made the source available for TPIE. I have put it here:  http://www.daimi.au.dk/~thomasm/tpie/larsthesis/

He suggests using the 'sanders' priority queue. Note that the code needs a lot of cleaning up and uses stxxl in places, which needs to go away.

[mgreve]

Kasper and I have added PQSequence3 from Lars Hvam Petersen's masters thesis. This is an implementation of Peter Sander's external priority queue from his article Fast Priority Queues for Cached Memory.

The priority consists of the following files in tpie/: priority_queue.h, priority_queue.inl pq_overflow_heap.h, pq_overflow_heap.inl pq_merge_heap.h, pq_merge_heap.inl pq_internal_heap.h, pq_internal_heap.inl

We fixed a couple of memory-allocation related bugs in the original source code, rewrote the internal heap, and all output going to stdout now goes to the logging system in TPIE.

A couple of tests are placed in test/test_priority_queue.cpp.

[thomasm]

The priority queue does not have doxygen comments. I don't think we should close this bug (or any other bug concerning new functionality) before everything is documented.