Changed closed_plus to match inf_plus from floyd_warshall_test, changed test to use closed_plus, fixed comments in documentation and replaced std::plus with closed_plus to match implementation, fixes #1164

[SVN r50808]

libs/graph

@@ -1 +1 @@
-Subproject commit 69d72805be149c2fabc93ac11b4ed26fa50cc327
+Subproject commit 968edbe972f500faa3f6b0e87b9dda9663e26e15