Revision 198450

First real step towards collapsing table borders.
border-collapse="collapse" rules implemented but not fully tested, yet.
Collapsing of borders works only for start and end borders, yet, and there only for non-spanned cells.
CellLM is now prepared to get the full list of grid unit it occupies (necessary for collapsed border painting).
Row.CellInfo extracted and renamed to GridUnit.
WIP...