Nested elements subvert white-space: nowrap

[Smylers]

With white-space: nowrap, WeasyPrint still allows wrapping at tag boundaries for nested elements within the text.

Demo: http://www.stripey.com/demo/weasyprint/nowrap_elements.html, which WeasyPrint (version 0.21) renders as: http://www.stripey.com/demo/weasyprint/nowrap_elements.pdf

@liZe already mentioned this in a comment to Issue #176, but it seemed worth having a separate number for this, so it's documented as a known issue.

[SimonSapin]

Thanks for properly filing and documenting this bug.

I believe that to fix this we’d have to keep track of the "last known line break opportunity" (which can be arbitrarily far in the tree of inline elements) and only "commit" stuff to a line up to that point so that we can "go back" when it turns out we’re overflowing the line. (I don’t know if that makes sense, but I can explain in more details if needed.)

[liZe]

Grouped in #301.

[liZe]

Fixed by closing #301.