[tlbuild] Testing net install

[Karl Berry]

Norbert,

    Fine. So what else tars do we have. Can the various builders please test
    their tar --version if that succeeds? Thanks.

Just eliminating the check on tar sounds like a better idea to me.
Our code should work with any tar, so it seems backwards to me to insert
a bunch of system dependent code purely to check if it's working.

Furthermore, the main reason that wget and lzmadec might fail is that we
ship our own binaries in some non-Windows cases, and we know for a fact
that these precompiled binaries will fail on old-enough user systems.
This is not the case (and does not need to be the case) for tar -- we
don't ship our own binaries for anything but Windows.

So let's not check tar.  Sorry I didn't realize this when we were
originally discussing the checking.

Thanks,
karl