Need of newer autoconf and libtool

[NIIBE Yutaka]

Forthcoming "Thread Plug-in Support" final patch #7, newer libtool is
needed (version 1.3d or later).  Because newer libtool has no
"ltconfig" script any more, we need newer autoconf to generate
"libtool" script.

We need newer libtool because we generate libguileqthreads.so which
is linked to libqthreads.so.  Such thing is not supported by libtool
1.3.5 (or younger).

Can I assume newer libtool and autoconf?  If not, I may postpone
"Thread Plug-in Support" final patch, but proceed to POSIX Thread
Support.  Well, I could just send it for your reference, not
intending the inclusion.

Opinion?
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