It is wrong to require autoconf, automake and libtool
on the used machine. You should be using "make
distcheck" to create self-contained distribution files.
But since you are using libtool, here's the fix that
allows using libtool 1.4. I also added versions up to
1.6 - I hope they won't break thing by then. Actually,
it's better to test for features, not for version
numbers, especially in the software that you distrubute
to the users (which is unfortunately the case for
autogen.sh in your build system).
The patch is against 0.9.14, but the problem is not
fixed in CVS yet.