options: sort --list-options

Until now, --list-options printed options in random order. There
literally wasn't any logic in its order, they just appeared as they were
declared. So just sort them.

Note that we can't sort them in advance, because for certain things
internal to m_config, the order actually matters.

Also we're using strcasecmp(), which is bad (locale dependent), but this
is output intended for human consumption, so it's not a problem.