rnd-20100326-2-src

* added image config suffix ".class" to be able to define classes of
  crumbled elements which are then separated against each others when
  drawing crumbled borders (class names can freely be defined)
* added image config suffix ".style" to use two new features for
  crumbled graphics:
  - "accurate_borders": try to draw correctly crumbled corners
  - "inner_corners": also draw inner corners -- this is a big kludge:
    number of frames for crumbled graphic must be "2", with the first
    frame as usual (crumbled graphic), while the second frame contains
    the inner corners for the crumbled graphic
  (These two features are mainly intended for bevelled walls, not for
  diggable elements like sand; "inner_corners" only reliably works for
  static walls, not for dynamically changing walls using CEs.)