Address code review comment: https://github.com/buildbot/buildbot/pull/673#issuecomment-15095930 and fall back to the .tac config location before calling loadConfig
Fix the way in which we fail with unfound configs to pass the unit tests. loadConfig must take a full path, not try to prepend the basedir, because it may take a fully qualified path as specified in the .tac.
Fix the "checking" message in upgrade-master to accommodate a config file from the .tac