derived classes' implementations of these functions become non virtual and
    can be truly _inlined_ for speed!  All GetPosition() in derived classes were also
    changed to return const wxPoint&, that is, a reference rather than a
    full copy of the position wxPoint. There was no need for polymorphism in
    {Get,Set}Position() since we never call these functions via generic pointer.
  * Remove BOARD::{Get,Set}Position() since they were only there to satisfy
    the pure virtuals established in BOARD_ITEM, which are now gone.
  * Added const wxPoint& CPolyLine::GetPos(), made CPolyLine::Get{X,Y}() inline.
  * Derive CPolyPt from wxPoint so we can return "const wxPoint&" fromt
    CPolyLine::GetPos().