There was a rule for command line switches, and for ini file options,
where in command line options words are separated with hyphen and in ini
files options are separated with underscore. This rule wasn't always
enforced, fixed it now.
Using url_file_attachment user can specify if he like to change objects
like 'file_share' marked as external (in Slack servers point of view)
to attachments, so the only value would be remembered URL for the
"uploaded" document as an attachment. Or, treat it as is, and let the
slack-backup to produce file which contain the URLs and corresponding
local file names for such files.
