bsdtar can't handle files >8GB

[Josh Carroll]

> Try the attached patch, which I think fixes this
> problem.

Tim,

The patch works great on RELENG_7, thanks for the effort! I'll let
someone else test it on 8-CURRENT :)

I created a 10GB file from /dev/urandom, tar'd it up and untar'd it,
and the md5s match:

MD5 (t/test) = 72db0cf41fa0872a586f52714a060b16
MD5 (tt/test) = 72db0cf41fa0872a586f52714a060b16

Thanks again,
Josh