[Bug 82397] Re: Use a more sensible message for "unknown" in permission tab.

[joelbryan]

For example, SELinux is not installed by default, the user will have to
install it, and enable it at boot-time configuration, so the user will
see the SELinux Context field to contain a valid selinux information,
but not in the case of Last Changed files, which will still display
"unknown" if the user haven't changed any permissions yet. I think the
"unknown" message is inconsistent and misleading the user to think it's
something else have to be installed just like the selinux information.

I think the approach is to change the unknown message to "No user
permissions had been defined" or better for both SELinux Context: and
Last Changed: labels.

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Use a more sensible message for "unknown" in permission tab.
https://launchpad.net/bugs/82397