Rewrite of bw in C++ -- part 1
Rewrite of bw in C++ -- part 1

This is only a beginning, but it's faster than the previous version
apparently. And a lot easier to maintain.

mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs