adding travel time based convergence criterion

git-svn-id: http://svn.code.sf.net/p/sumo/code/trunk/sumo@16646 29f149b2-0c63-11e1-8f5c-a347f6a9acd0
adding test for travel time based convergence, refs #21

git-svn-id: http://svn.code.sf.net/p/sumo/code/trunk/sumo@16647 29f149b2-0c63-11e1-8f5c-a347f6a9acd0