Under FreeBSD, as annoying as it is, switches must directly follow the
command or subcommand in question, and cannot come after actual payload
argument. Calling `zpool get all -H` instead of `zpool get -H all`
caused error messages to be spewed to the console under FreeBSD when
simply completing `zfs <TAB>`, this should fix that. The change should
also be compatible with other operating systems (namely Linux) that
don't have this requirement, as they (generally) allow arguments to come
before _or_ after the primary non-switch argument (though I do not have
access to a zfs-enabled Linux machine to test this).
