johnson_all_pairs_shortest.hpp: When writing into the distance map, we need

to subtract one from the index in graph g2, which has an extra vertex "s" at
the beginning. Amazing how long this bug persisted...


[SVN r24044]

libs/graph

@@ -1 +1 @@
-Subproject commit db84792f9f813966e5c8c4117883f3886383dcca
+Subproject commit 008a8c71686da7a9d5ea7872378b406878babe0c