Made some of changes from #9246: added new test case (modifying tests on callback usage to match current documentation); removed special-casing of empty graphs; added patch from #9246 for correct return values; did not make change to documentation suggested there since I chose to have the callback called even for empty graphs; fixes #9246

git-svn-id: http://svn.boost.org/svn/boost/trunk@86336 b8fc166d-592f-0410-95f2-cb63ce0dd405