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