[css3-background] border-radius and wrapping inline elements

The specification does not currently define how rounded corners are rendered for inline elements when the latter wrap, especially when there is not enough room left on the line to render the full curve. Today some implementations use the remaining width on the line for their calculation for instance. Similar issues likely happen for border-image.

I do not have a well-formed opinion on the importance of the scenario for authors or its most desirable rendering. But I would suggest we explicitly call this out as undefined for completeness of this level of the specification.