bug#20713: aclocal/tar.m4 and solaris 5.10

[Karl Berry]

    should we change "unknown" to $GID & $UID respectively ?

I guess it couldn't hurt, although I doubt it makes any difference in
practice.

    if test $am_uid = "unknown"; then

Don't we usually avoid quoting constant strings? I.e.:
if test "$am_uid" = unknown; then

      AC_MSG_WARN([ancient id detected; assuming current UID is ok, but 
dist-ustar might not work])

"Might"? Either it works or it doesn't? Anyway, who ever uses ustar?
Never seen it.

Anyway, seems like such a warning "might" be useful when producing an
archive with automake (running make dist), but not when running
configure. When merely doing "./configure && make", ustar is irrelevant.

Anyway #2, I think the chances of someone wanting to produce a ustar
archive on a system with old id is zero.

Thus I suggest just fixing the syntax stuff and letting it go at that. 

    the point of the checks isn't just to annoy the user.

No :)? That's what it seems like. Helpful to the package developer;
annoyance to the configure user. -k