Modify the [check] phase in client.inc to only fail when adding non-unix line endings

Currently, the check phase errors out if any non-unix line endings are found in a patch file.

      $contents = file_get_contents($file);
      if (strpos($contents, "\r") !== FALSE) {
        $this->set_error(array('@filename' => basename($file)));
        break;
      }

However, we should allow a test to run if the non-unix line endings are being 'removed' via a patch file.

Suggested approach would be to read the file line by line, and if \r found, check for a '-' at the beginning of that line before throwing an error.