[boost] [1.34.1] [Graph] Fix overflow handling in shortest-path algorithms (#1009)

From: Douglas Gregor (doug.gregor_at_[hidden])
Date: 2007-05-29 11:40:10

Trac ticket #1009 describes a bad, longstanding bug in the Graph
library's handling of overflow in shortest-paths algorithms:

  http://svn.boost.org/trac/boost/ticket/1009

I would like the attached patch (also attached to the ticket) to be
considered for 1.34.1. The problem manifests itself as a bug in the
Bellman-Ford algorithm (and probably others), making them produce
incorrect results, such as the one reported here:

  http://listarchives.boost.org/boost-users/2007/05/28205.php

The fix is simple, relatively low-risk, fully tested on Linux with GCC
4.1.1, and solves a rather embarrassing problem in the BGL.

        - Doug