freebsd-version(1): Add -j flag to support jails

[kfv_kfv.io]

Summary

Make freebsd-version(1) support jails by adding the -j flag which takes jail jid or name as an argument.

[bcr]

OK from manpages. A useful feature, I might add.

[kevans]

bin/freebsd-version/freebsd-version.sh.in

120

We should probably warn if $opt_j == 1 already, but as a future addition it'd be neat if we could support manually-driven usage like:

freebsd-version -j1 -j2 -j3

to fetch the versions of multiple jails, but I don't think that's important to do up front.

[kfv_kfv.io]

• freebsd-version(1): accept multiple occurrences of the -j option

[kfv_kfv.io]

bin/freebsd-version/freebsd-version.sh.in

120

I just took care of that, but I didn't know if I should eliminate duplicates, so the user can currently do something like:

freebsd-version -j1 -j1 -j2 -j1

And in return, we give them the versions in the same order as specified.
Please let me know if I should change this behaviour.

[kfv_kfv.io]

@kevans: by the way, on the subject of the attribution we discussed in IRC, I prefer Faraz Vahedi <[e-mail]>, thanks!