Add a new --jail option to the pkgbase script which installs
jail-specific set variants if they exist:
- "minimal" is replaced with "minimal-jail"
- For sets shown in the component selection dialogue, only show the appropriate variant (jail or non-jail) for the target.
- --jail implies --no-kernel, so the kernel also won't be installed in a jail.
Modify the jail script to pass --jail to the pkgbase script.
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