Added check for valid duplicity-backup configuration file. Corrected a logic error with logging to a file. NOTE! Changed the order of backup config parameters! WAS: target dir, configfile, [remote check file], NOW: configfile, target dir, [remote check file]. This is more logical since the backups are driven by duplicity-backup config files, and because the remote check file (when defined) resides at the target directory. Corrected few typos.