Merge branch 'dd/help-autocorrect-never'

"git $cmd $args", when $cmd is not a recognised subcommand, by default tries to see if $cmd is a typo of an existing subcommand and optionally executes the corrected command if there is only one possibility, depending on the setting of help.autocorrect; the users can now disable the whole thing, including the cycles spent to find a likely typo, by setting the configuration variable to 'never'. * dd/help-autocorrect-never: help.c: help.autocorrect=never means "do not compute suggestions"