Benchmarks for the qp-trie

Benchmarks for the qp-trie

The main benchmark is `qpmulti`, which exercizes the qp-trie
transactional API with differing numbers of threads and differing data
sizes, to get some idea of how its performance scales.

The `load-names` benchmark compares the times to populate and query
and the memory used by various BIND data structures: qp-trie, hash
table (chained), hash map (closed), and red-black tree.

The `qp-dump` program is a test utility rather than a benchmark. It
populates a qp-trie and prints it out, either in an ad-hoc text
format, or as input to the graphviz `dot` program.