[Eric] eric4 indentation

[Dan]

When using a monospaced font (set via Settings / Prefs / Editor /
Style / Use Monospaced by default), the indentation guidelines become
misaligned with the code.

I have no idea why the monospaced font is not the default for
programs, as in all other IDEs I have seen, but at least the vertical
guidelines should respect my preference once I set it.

This is eric 4.5.7 on Linux (with a truetype monospaced font)