If installing from a pmax diskimage as both current root and target root,
the diskimage /usr/bin/tar is hidden underneath the target /usr mountpoint
when it's time to untar distribution files. From a comment in the change:
Make sure any binaries in a diskimage /usrbin get copied
into the current root's /usr/bin. (may be same as target /usr/bin.)
The rest of sysinst uses /usr/bin/{tar,ftp,chgrp}.
We cannot ship those in /usr/bin, because if we did
an install with target root == current root, they'd
be be hidden under the target's /usr filesystem.
Requires updated diskimage build script which populates /usrbin with
tar, gzip, gunzip, ftp, and chgrp (all statically linked.)