look-back distance needs to be increased by the length of the ego vehicle. This fixes most remaining collisions in b50 (which contains very long vehicles) refs #1401

git-svn-id: http://svn.code.sf.net/p/sumo/code/trunk/sumo@16895 29f149b2-0c63-11e1-8f5c-a347f6a9acd0
fixing collisions in b50 caused by unsafe insertion. fix #1401 (until further notice)

git-svn-id: http://svn.code.sf.net/p/sumo/code/trunk/sumo@16896 29f149b2-0c63-11e1-8f5c-a347f6a9acd0