gnupload touchups.

gnupload touchups.

* lib/gnupload (conffile): New variable.  Use throughout.
(dry_run): Use `false' and `:' values.  Show, don't execute,
gpg signing commands upon --dry-run.
(usage): Typo and formatting fixes.  Mention that commands are
applied in order.
(argument loop): Factorize a bit, fix quoting.
(dprint, mkdirective, mksymlink, upload): Formatting and
portability fixes.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>