Now that CAN-2003-0689 is published officially, we need to make possible

Now that CAN-2003-0689 is published officially, we need to make possible
to build on systems with fixed getgrouplist() in GNU libc < 2.3.2.
Unfortunately, we can't detect correctness of getgrouplist() functioning in
portable way so this is left up to developer/packager.

This patch adds --with-good-getgrouplist[=no] switch to configure which packagers
on Linux platforms could use to specify in their own builds if they now that glibc
on their platform is fixed w.r.t CAN-2003-0689. By default we still think that glibc
is vulnerable and perform our version check.

** This patch does not change default behaviour in Samba 3.0 -- by default we are not
vulnerable on glibc as we are not using getgrouplist()

See http://www.securityfocus.com/bid/8477 for vulnerability description.

Right now there are following Linux vendors released glibc updates for CAN-2003-0689:

RedHat -- https://rhn.redhat.com/errata/RHSA-2003-249.html
ALTLinux -- http://www.altlinux.com/index.php?module=sisyphus&package=glibc