rnd-20040118-1-src

* custom elements can change (limited) or leave (unlimited) elements
* added new start movement type "previous" for continued CE movement
* added new start movement type "random" for random CE movement start
* added new element "sokoban_field_player" needed for Sokoban levels
  (thanks to Ed Booker for pointing this out!)
* added elements that can be digged or left behind by custom elements
* added group elements for multiple matches and random element creation
* fixed some graphical errors displayed in old levels
* fixed wrong double speed movement after passing closing gates