Indentation must be measured in units of the surrounding text,

Indentation must be measured in units of the surrounding text,
not in units of the contained text.  Consequently, "display"
and "lit" class tags must not be on the same element:  First,
"display" must set up the indentation, still using the outer
units, and only after that, "lit" may change the font.

This fixes .Bd -literal which got the wrong indentation.
Bug reported by tb@.