* doc/autoconf.texi (Integer Overflow): Greatly expand and

* doc/autoconf.texi (Integer Overflow): Greatly expand and
rewrite, taking notions from the recent discussion on the gcc and
autoconf mailing lists; please see
http://lists.gnu.org/archive/html/autoconf-patches/2006-12/msg00091.html
and follow the many links.
(Integer Overflow Basics, Signed Overflow Examples):
(Optimization and Wraparound, Signed Overflow Advice):
(Signed Integer Division): New sections.

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