Some patches from James H:
 - reinstate the initialisation of ds->w and ds->h in guess.c, which
   I'd accidentally removed during game_size() refactoring
 - reorganise Net's interpret_move() so that my uncommitted patch
   for drag-based UI (which he uses on the Palm port) will apply
   more easily
 - the interpret_move() changes make it easy to have a single move
   type which rotates a tile by 180 degrees, so this is now provided
   via the `F' key (but there's no spare button available to provide
   it via the mouse).

[originally from svn r6070]