LFI Scanner : Fix headers bug + find_root() and improved a bit detection and leak

headers bug:
- headers would all be removed and thus the default headers set wouldn't
  be taken into account

find_root() buf fix:
- It wouldn't find the root_path if there is an extension or something
  else appended to our page_name. self.url_suffix is thus appended to
  fix this
- Store dir_traversals to attain the root path

detection improvement:
- if a PHP script were to include links to our URL in the body of the
  page : false positive. In order to avoid this false positive, we check
  for function.include which shows when error messages are activated

leak improvement:
- add test for direct injection if php://filter fail