Only for linux-x86_64 for now, as it fails to build on linux-i686.

To provide a more "high level" view of progress, don't output build logs
of each componets on stdout, but write them in files in the logs/ directory.

This idea was suggested by mcs and Kathy in this comment:
https://trac.torproject.org/projects/tor/ticket/17379#comment:12

Update rbm and add example rbm.local.conf file.