linespacing methods fixed and fit-glyph assume everything is text

[simoncozens]

Images / other boxes height is not being taken into account.

Test case:

\begin{document}
\script[src=packages/linespacing]
\script[src=packages/lorem]
\script[src=packages/image]
\set[parameter=linespacing.method, value=fixed]
\lorem[words=150]
\img[src=documentation/fig1.png,height=120pt]
\end{document}