Add support for .pkg

[ci-macpaw]

Originally reported on Google Code with ID 276

paracelsus:

.pkg is just a bundle containing other archives, but it would be useful to figure out
a way to handle accepting directories and then return the files inside identified as
archives.

[ci-macpaw]

atr000:

And this has most/part of it done. mpkg would require reading the manifest itself and
then going through each pkg indivudually

http://github.com/hac/payloadextractor/

[ci-macpaw]

atr000:

Beyond pacifist, it is basically that:

http://www.timdoug.com/unpkg/

mpkg can get messy too

[ci-macpaw]

d235j.1:

Newer versions of .pkg (for OS 10.5 or newer) are actually xar-compressed archives.

[MaddTheSane]

I'd also like to extract .pkg files created for NeXTStep/OpenStep.