Following discussions with Gilles Morris [1], it seems that it is preferable to
use several blacklist files in a blacklists/ directory. It is easier to add an
unversioned file for experiments than modifying a tracked file.
Also fall back to a simpler syntax, giving up ConfigParser, now that section
names are not needed anymore.
And allow --blacklist parameter to be a complete path, instead of only one
of the filenames contained in tests/blacklists/
[1] http://www.selenic.com/pipermail/mercurial-devel/2009-December/017317.html
