[LH1630] Indicate non-breaking spaces in "Show Invisibles"-Mode

Maybe not directly a bug, but at least to me it is very puzzling that I cannot tell a normal space and a non-breaking space apart when “Show Invisibles” is activated. Maybe non-breaking spaces could use another symbol, e.g. [size=200]¬[/size] instead of [size=200]·[/size]?

This has been filed. Thanks!