Allow additional header lines in bandwidth measurements documents
As commented by teor in: https://github.com/pastly/simple-bw-scanner/pull/112#issuecomment-385108911
get it backported to 0.2.9 and later. I think Tor should only warn if: an incomplete line contains a "bw=" key an incomplete line contains a "node_id=" key an incomplete line occurs after the first complete line