Several cpio bugfixes spotted by Isaac Dunham.
Promote cpio out of pending.

After some waffling I put it in "posix", even though it was last specified in
susv2 (where it was the obsolete 6 byte header entries predating susv4).

LSB specifies it, including the 8 byte header fields, but for the actual
command it just references SUSv2. (LSB isn't so much a standard as Red Hat's
"notes to self".)
More cpio bugfixes from Isaac Dunham.

Fix FLAG_o to actually be 1 like the comment says, don't try to strlen(name) before reading it, pad TRAILER!!! entry correctly.