tar: format 'ustar' cannot support UID/GID longer than 21 bits

tar: format 'ustar' cannot support UID/GID longer than 21 bits

See automake bug#8343 and bug#13588.

POSIX 1988 'ustar' format is defined with *fixed-size* fields. There
is notably a 21 bits limit (2097151) for the UID and the GID.

Tom Rini tom_rini@mentor.com says (in bug#8343):

    When the user has a UID or GID that is larger than the ustar format
    supports, pax does not error out gracefully in some cases (FC13).

Marc Herbert <marc.herbert@intel.com> adds (in bug#8343):

    When "configure" is run by a user with an UID bigger than 21 bits,
    BSD pax 3.4 aborts when trying to create the 'conftest.tar' test
    archive and leaves an empty or corrupted conftest.tar file behind.
    In the next step, pax tries to extract this incomplete or corrupted
    archive and this *** hangs the whole ./configure script ***.

    Note: GNU cpio 2.9 pretends to pass the test but it is a LIE: it
    silently truncates any big UID to its lower 21 bits. I don't know
    what can be the consequences of this lie.

    I think there is currently a design issue in automake/m4/tar.m4
    considering that a ustar archive should should *never* succeed when
    ./configure is run from a big user ID.

Months later, Petr Hracek <phracek@redhat.com> reports a similar issue
(in bug#13588) for Fedora 17:

    I am trying to solve problem in case a user is created with big
    UID and during configuration pax hangs with message

        ATTENTION! pax archive volume change required.
        Ready for archive volume: 1
        Input archive name or "." to quit pax.
        Archive name >

    and needs user interaction.

    Reference: <https://bugzilla.redhat.com/show_bug.cgi?id=843376>

Time to fix this issue, on the line of a preliminary patch provided by
Petr Hracek in bug#13588.  The final patch ended up being remarkably
different from that original proposition, though.

* m4/tar.m4 (_AM_PROG_TAR): If the UID or GID of the current user is
too high (> 2097151), the 'ustar' format cannot work.  Adjust checks
accordingly.  Some related code reordering and clean-up.
* t/tar-ustar-id-too-high.sh: New test.
* t/list-of-tests.mk: Add it.
* t/tar.sh: While at it, tweak and enhance a little.
* t/tar2.sh: Likewise.
* t/tar3.sh: Likewise.
* t/tar-override.sh: Likewise.
* NEWS: Update.
* THANKS: Likewise.

Helped-by: Pavel Raiskup <praiskup@redhat.com>
Helped-by: Petr Hracek <phracek@redhat.com>
Helped-by: Marc Herbert <marc.herbert@intel.com>
Helped-by: Tom Rini <tom_rini@mentor.com>
Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>