Smaller (performance) issues

Hi, had one performance-issue (check_displayport) and 2 small other issues -> see my PR. Feel free to ask for more information.

The powershell-problem would also apply to x11docker: https://github.com/mviereck/x11docker/blob/f17a7d248dfab24f82fd5a67840e459028db9593/x11docker#L1296