fixing speed when converting to ns2 output

git-svn-id: http://svn.code.sf.net/p/sumo/code/trunk/sumo@15337 29f149b2-0c63-11e1-8f5c-a347f6a9acd0
implemented #998 (only import tag 'ele')

git-svn-id: http://svn.code.sf.net/p/sumo/code/trunk/sumo@15338 29f149b2-0c63-11e1-8f5c-a347f6a9acd0