The attached patch seems to fix the worst problems.

I’m marking up each line in a message with a “span” tag and a “line”
class; then I use CSS to visually separate the lines.  Simple browsers
that don’t support this CSS rely on “span” to be an inline tag; likewise
they rely on “div” to be a block tag, no matter what the CSS might say.

So the attached patch changes the tag from “span” to “div”, so simple
browsers will render each line on their own instead of joining them.
This seems to have no negative impact on the rendering in other
browsers.  It also shouldn’t be a problem going forward, as popular
powerful browsers allow me to style these “div” tags without
limitations.

What do you think?

-- 
Ricardo