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<!-- If possible, test if the latest release is affected too. -->

## Summary

<!-- general description of the problem -->

## Steps to reproduce

 1. 
 2. 
 3. 

## Actual result

## Expected result

## Environment

<!-- replace the comments with the output of the commands -->

 * Operating system: <!-- uname -a or lsb_release -a: Debian GNU/Linux 9.1 (stretch), Windows 7, Ubuntu Xenial, etc -->
 * Linkchecker version: <!-- linkchecker --version -->
 * Python version: <!-- python --version -->
 * Install method: <!-- distribution package, PyPI, from source tarball, from git, etc -->
 * Site URL: <!-- e.g. https://example.com/... -->

## Configuration file

<!-- include full contents of your configuration file, ~/.linkchecker/linkcheckerrc -->

## Logs

<!-- Include full log of the linkchecker run, with --verbose -->
<!-- Also include the exact commandline used -->
<!-- If a Traceback happened include it in full as well -->

## Other notes

<!-- Ideas on what might have caused this or could fix this are welcome of
course. -->
