flagging network files correctly to prevent validation if not explicitly wanted, refs #1164

git-svn-id: http://svn.code.sf.net/p/sumo/code/trunk/sumo@15713 29f149b2-0c63-11e1-8f5c-a347f6a9acd0
new netconvert option in internal meta tests, refs #21

git-svn-id: http://svn.code.sf.net/p/sumo/code/trunk/sumo@15714 29f149b2-0c63-11e1-8f5c-a347f6a9acd0