The 'make signtag-release' and 'make signtag-alpha' commands can be
used to tag a stable or alpha release using the version informations
from rbm.conf.

And buildconf/nb_procs to buildconf/num_procs.

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.