respect Linux capabilities(7) in cache

[anarcat]

The default GNU tar configuration does not carry fancy extended
attributes and that is where, among other things, stuff like Linux
capabilities(7) are stored. This is kind of important because that's
how ping(8) works for regular users.

We shove --selinux and --acls in there while we're at it, because why
not. We never know what the future might bring, and it seems
silly not to create a complete archive.

Note that --xattrs-include='*' is important because, by default, GNU
tar will not include capabilities /even/ if --xattrs is specified on
the commandline, see this bug report for details:

https://bugzilla.redhat.com/show_bug.cgi?id=771927

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[anarcat]

i do not have or wish to have a google account, but do whatever with my code already and just fix this bug. ktxbye.

[anarcat]

ping.

[iustin]

Unfortunately until the split from Google is finalized, we can't merge this without signing the CLA. I'm surprised one need a google account for it though, I thought you can sign with any email address…

[anarcat]

how about i release this in the public domain, CC0, or whatever, and someone else picks it up and commits it?

i regret opening that PR in the first place now :(

[saschalucas]

@anarcat: i would pick it up and proxy-PR it for you. I totally understand to reject singing CLAs. THX Sascha.

[saschalucas]

I've proxy-PRed this PR in #7. probably this can be closed? thanks sascha.