Change the quirks mode text-decoration code (soon to be used for all
modes) to follow CSS 2.1's rules for positioning of decoration lines.
Decorations are now drawn at a constant vertical position established by
the element creating the decoration, and more than one of the same type
(underline, overline, line-through) of decoration are supported on the
same piece of text.
This means that text-decorations can now significantly overflow a text
frame, since the vertical-alignment of the element with text-decoration
may be substantially different from the vertical alignment of the text.
Set overflow areas for text frames with text decorations in
nsLineLayout::RelativePositionFrames since it must happen *after*
vertical alignment is done, and when relative positioning data are
consistent (nsIFrame::GetRelativeOffset matches the offset that has been
applied).
